Overview: This is a very powerful, high-survivability, Regeneration-stacking Engineer build. With this build I am 100% confident in winning any 1-on-1 confrontation in WvW, and quite confident and winning any 1-on-2 or even 1-on-3 fight. This build is tanky enough to be able to take Supply Camps solo. It is also extremely effective in PVE and in Dungeons, with a little on-the-fly tweaking (listed below) it can fulfill any role. I have been very successful as the main tank for COF Path 1 runs, with no heavy armor classes.
Strategies/Rotations: I've included the overall strategies/rotations at the bottom of this guide, below the details on Gear/Rune/Sigils/Skills/Traits. Jump down there if you want the meat.
Food/Nourishment: I eat Mango Pies for the Regeneration/second, which stacks with the Regeneration boon, Backpack Regenerator, and the "Regeneration" from auto attacking with Elixir-Infused bombs. For nourishment I use Quality Sharpening stones for most content, and relevant potions for dungeons. If you have enough of them, for especially tricky content you can throw on a Regeneration booster for even more stacked Regen.
Gear: I run full Cleric's gear. The Toughness and Healing Power benefits are very obvious as you get used to this build. With the exception of Speed Runes, you don't want too much Vitality in this build, as each point of Vitality (over Toughness) reduces the value of all the Regeneration you'll have.
Sigil: I started out with a Sigil of Life for a long time. It would definitely be my permanent choice if the 25 stacks persisted when zoning, but because they go away, I've since switched to the Sigil of Energy for a more reliable effect. And damn, is it reliable! Now that weapon swap sigils work with kits, with the way this build plays you will be guaranteed to pop the +50% energy on its 9 second cooldown, giving you an extra dodge every 10 seconds. For reference, you typically get one dodge every 10 seconds, so this can double your dodges! This build really takes advantage of the effect; if you are playing right you will never be in one kit longer than 10 seconds anyway.
Rune: I bought Runes of Speed to assist with World Completion, but they actually make a huge difference in combat with this build. Bombs are the best weapon in the game for kiting, and anything that increases your move speed increases how well you can kite in both PVE and PVP. The +7% Move speed while using Swiftness (for a total +40% move speed) does not go unnoticed, and the extra Swiftness duration means you can have Swiftness permanently activated without requiring the Speedy Kits trait. I wish the extra Vitality were Toughness, but I suppose it helps a little with dealing with conditions. The next best rune set I would select would be a set of Runes of the Dolyak, for yet another stacking regeneration effect, but the extra speed gives you a huge edge when kiting.
Healing Skill: I switch between the Healing Turret and Med Kit depending on what I am doing. The Med Kit is definitely going to be your default travel kit because of the Swiftness on skill 5, and it is also the best choice when you are going to be kiting (COF Path 2 "Protect Magg" room, for instance, or taking a WvW Supply Camp solo). Since you can kite and attack with bombs constantly anyway, it is never a problem to switch to the healing kit and quickly take out a condition, get 3 small heals, and some extra swiftness/Fury. If you do not need to kite or travel though--for example, in an easy dungeon like COF Path 1--ditch the Med Kit for the Healing Turret. You'll mostly want the turret for its blast finisher so you can grant Area Might with the Incendiary Bomb, see the bomb kit section below. You'll deploy it and instantly blow it up for value on cooldown.
Utility 1 [Elixir C / Elixir Gun]: I switch between Elixir C and the Elixir Gun depending on my situation (and change my Grandmaster Alchemy trait to go along with it, see traits below). Elixir C is more appropriate when you are dealing with a lot of conditions all the time, such as in WvW or when gathering in Orr. Although there is condition removal with the Elixir Gun, Elixir C is simply faster and more efficient in most cases. If you don't expect constant conditions, the Elixir Gun adds a lot of utility--so much so that I will go into detail on each skill below, regarding how it should be used in this build:
Elixir F (Gun Skill 2): This ability can be used to give yourself even more Swiftness, and when combined with everything else in this build can result in having 120+ seconds of swiftness at a time!
Fumigate (Gun Skill 3): This is an amazing skill that can clear conditions from your entire team, but the Poison can be a huge help on fights with healing enemies, such as the final boss of COF Path 1.
Acid Bomb (Gun Skill 4): This skill is AMAZING for traveling, but it requires some finesse. I have "About Face" bound to a mouse button, and while autorunning I will quickly hit the About Face button and almost immediately afterward activate this skill. This will cause your character to quickly turn around and then propel forward, and you can continue their auto run by moving the camera back during the skill animation. It is tricky to perform but a huge boon when escaping in WvW.
Super Elixir (Gun Skill 5): You should toss this down whenever you can for even more regeneration for your tanking, and with projectiles it will help clear conditions, too.
Utility 2 [Bomb Kit]: This is the bread and butter of the build, and with Elixir-Infused Bombs and increased Bomb Radius it is a powerhouse.
Bomb: Your auto attack take a split second to activate but damages everything in PBAOE range, which makes it great for kiting, or dealing with anything that is difficult to target. You will almost never need to worry about kiting anything using this build.
Fire Bomb: Using Fire Bomb correctly is extremely important as it creates a Fire Field that can be used to grant many stacks of Area Might, as well as to get yourself a Fire Shield. To get the best use of Fire Bomb, you can set down Big Ol' Bomb immediately before casting it, then cast Fire Bomb. The timer on Big ol' Bomb is such that it will explode just in time to grant Area Might with the Fire Bomb. You can then deploy and explode your turret (or wisely, deploy your turret before setting the Fire bomb) and even bring in your supply drop for two more Area Might effects. If you still have time I always take this opportunity to drop my bomb kit and use Rifle Skill 5 (Jump Shot) on myself to gain Fire Aura and give the enemies 6 stacks of Vulnerability, and then I switch immediately back to the Bomb Kit. It's this constantly swapping between the Rifle and Bomb Kit for the Fire Aura combo that will also guarantee that you are activating the Sigil of Energy effectively on cooldown.
Concussion Bomb: I typically use this bomb on cooldown, as confusion is always helpful, but it can be used tactically in certain fights such as against the final boss of the Snow Fractal, immediately before he teleports to the top of the room.
Smoke Bomb: This skill is extremely helpful for tanking as it will effectively keep all enemies in its radius blinded, and even more so if people are shooting projectiles into it. It can also be used to stealth yourself in a pinch when combined with Jump Shot or any of your blast finishers. This is useful in PVE if you need to drop aggro for some reason, as the stealth is very short and will go away almost immediately. I've also used Smoke Bomb with a party to avoid enemy invaders in WvW, by timing a huge string of blast finishers to get 15+ seconds of Area Stealth to everyone.
Glue Bomb: This skill is most useful when running away, or when applied to an already incapacitated opponent. I would avoid using it on cooldown and save it for when you need to flee from melee (drop it, dodge, and run) or when you are tanking and need enemies to stay close to you. This is very useful when fleeing from enemy players, drop it on cooldown and it will add an obstacle that will make it harder for the enemy to catch up to you--even if they roll through it or otherwise avoid it, having to deal with it gives you an advantage.
Big Ol' Bomb: This is one of the most raw damaging attacks in the game and it is extremely powerful. As noted above you will use this on cooldown for its Blast Finisher with Fire Bomb to keep up stacks of Might, but it can also be used for Stealth with the Smoke Bomb. The knockback can actually be detrimental in PVE as with bombs PBAOE you will typically want enemies to be near you, not far from you--so use with care when facing ranged enemies. For that reason when fighting trash PVE enemies I try to save this skill so that it will finish off all the enemies it hits. This is very useful in WvW for knocking enemies off cliffs along with the Overcharged Shot (Rifle 4) and can and should be saved for that purpose. It's also great for area denial, or for running into an enemy Zerg, dropping it, and running away.
Utility 3 [Elixir B]: I simply have not found an alternative to this skill; it is a great ability. You should more or less be using both the Elixir and the Toss Elixir toolbelt skill on cooldown for the provided buffs, the benefits of which are greatly increased with the HGH Trait. Note however in the traits section below that when option for the Elixir Gun over the Elixir C, the HGH trait is less useful--you should swap it out for Cleaning Formula 409 so you can retain some immediate condition removal. If you do this, I would be more careful using Elixir B on cooldown and save it for condition removal, too. While this is a very powerful skill I do feel it is the weakest skill in the build, however the immediate "fire and forget" benefit is too valuable to trade for something like another kit, which would likely be too situationally beneficial. If you are going to experiment with changing this build I would start with this Elixir B.
Elite Skill [Supply Drop]: I would love to try out Elixir X or Mortar but neither of them can really hold a candle to Supply Drop. This is the best Engineer Elite and the most effective, and it can even be used as another Blast Finisher for stacking Area Might. You should never cast this without taking advantage of the Area Might. This skill can be invaluable for pushing you to victory on challenges like taking a supply camp solo, as the Med Kits can be carefully rationed. The turrets also draw a lot of enemy fire and can help you to recover while kiting.
Rifle Skill 1 (Hip Shot): Your rifle auto attack should almost never be used, except when you are in a situation where you need to stay out of melee range, or when finishing off a fleeing WvW opponent. It's simply not as good as your Bomb auto attack, so avoid using it when you don't have to. If you have the Elixir Gun, seriously don't even use this skill at all--use the Elixir Gun auto attack if you have to fight at range, as the conditions will be more useful.
Rifle Skill 2 (Net Shot): You will be dropping the bomb kit to throw out your net very frequently in WvW, and in some difficult PVE content too. In a typical situation you might switch to the Rifle, hit 2 for net shot, and then instantly swap back to Bomb Kit; almost like a Utility Skill.
Rifle Skill 3 (Blunderbuss): I do actually use this skill occasionally when I am already in rifle and very close to an enemy for the Bleed, but it is not mandatory. For example, after I have done the Fire Bomb + Jump Shot combo, I will frequently tap 3 for Blunderbuss quickly before swapping back into the Bomb Kit, as the Bleed is fire-and-forget. I wouldn't bother with this at all if you are out of melee range, though.
Rifle Skill 4 (Overcharged Shot): This is an amazing skill and I use it just like a utility skill, similar to Net Shot above. Some its most notable uses include interrupting enemy heals, especially the heal Veteran Guard NPCs in WvW use. It also works to interrupt the Dredge Fractal boss' heal. It's even great for stopping enemy players from running away from you, as being suddenly knocked down at range by a melee bomb-wielder can be very disorienting for most players, and therefore almost never dodged. You can also use this skill combined with Big Ol' Bomb to murder griefers in the Eternal Battlegrounds jumping puzzle (or any high-up area) by circle strafe/kiting until their back is to a ledge, then popping this to send them to their deaths! I've won 1v5 fights using this skill at great heights. The personal knockback is strictly a disadvantage, I think, but one that is worth paying for the power of the skill. There is a corner escape case where you can use it similarly to the Elixir Gun's Acid Bomb where you about face, activate, and mouse turn to face forward, but this can be very tricky to pull off, and if it doesn't connect will actually put you at a disadvantage to escape.
Rifle Skill 5 (Jump Shot): This will probably be your most-used Rifle ability and the biggest draw away from Pistol/Pistol or Pistol/Shield. The 6 stacks of instant vulnerability it applies are nothing to scoff at, but the real utility is the movement itself. You can use this as a gap closer, or to flee, or to give yourself Fire Aura or Stealth from your Fire or Smoke Bombs. It's a huge utility help in Jumping Puzzles as it lets you jump places that are typically inaccessible with normal jumps (only at horizontal distances though, you can't get much vertical height with it). One neat use of the ability is to confuse mob AI; for example in COF Path 1 in the Acolytes event, you can kite a bunch of enemies to any of the three ledges in the back of the room and then Jump Shot from one ledge to another ledge. This seems to confuse the enemies' Pathfinding and they will disengage from you; but you will have wasted their precious time chasing you and saved your party members some grief!
Traits: Traits are selected to maximize survivability over damage, I will go over each of the selected major traits below.
Explosions Adept [Forceful Explosions]: This is a very useful trait for this build as the additional range is fairly substantial and can make a huge difference in PVE, PVP, and Dungeons--especially for the utility bombs. It also increases the radius for applying healing to your allies, who will typically not be stacking right on top of you, which is typically required for the effect without this trait. If I had to swap out this trait I'd experiment with Shrapnel instead.
Inventions Adept [Protective Shield]: This is a very difficult trait to select, in my opinion, because there is no clear "most powerful" effect for this build. I typically go with Protective Shield as it provides the least situational benefit. I will always switch this to Explosive Descent in WvW and world completion for the reduced falling damage. Energized Armor is also a fine selection which is perhaps even less situational than Protective Shield, but I tend to prefer tanking effects over damaging ones (if you survive long enough, they'll die eventually!) Cloaking Device can also be nice as it will confuse enemies in WvW to allow you to escape and continue kiting, and drop aggro in PVE--but you might not want that if you are tanking in PVE! Stabilized Armor really isn't the best choice since this build really wants you to be moving and dodging constantly, although it could be useful in easy trash PVE content scenarios.
Alchemy Adept [Self-Regulating Defenses]: This is an invaluable skill for a tank and it offers a lot of survivability. The Warrior has an equivalent trait which activates Endure Pain at 25% health--but it's at Grandmaster level! You simply cannot pass up this sort of value. Since you can still use utility skills under the effects of Elixir S you can immediately switch right back to your bombs while you are shrunken and keep attacking, although it will keep you out of your Toolbelt for the duration. If things are looking particularly dire you can switch to your Med Kit instead, clear your conditions, and heal back up while running away. You can continue to revive downed players while invulnerable, and it is great for wasting enemy cooldowns and allowing your own cooldowns to clear. I wouldn't get rid of this in any mode of play.
Inventions Master (Power Shoes): This is a must-have trait for this build and I would never swap it out for anything else. After playing an Engineer with this trait for any length of time, being forced into combat on any other class will feel ungodly sluggish to you. This comes very close to letting you run at normal speed while in Combat, which is a massive boon when kiting or fleeing. I say all this even though the trait doesn't stack with Swiftness, for which you should have close to 100% uptime. Without this trait you would be forced to have 100% uptime on Swiftness to be at your most efficient, which would force you to occasionally forgo doing additional damage or applying a condition at the right time in favor of keeping the boon up. This is a very reliable trait for those situations.
Alchemy Master [Backpack Regenerator]: This is a must-have trait for this build, the regeneration is not the Regeneration boon, and so it stacks with that boon. This build revolves around stacking a ton of Regeneration, and the numbers are great for this trait. Equip it and never let it go.
Inventions Grandmaster [Elixir-Infused Bombs]: This is the bread-and-butter of the Bomberman Tank build and really defines the build; it causes all of your bombs to heal for around 250 HP each in PBAOE; this effectively like adding yet another form of stacking Regeneration as you will be dropping bombs constantly. In most fights even against many opponents your health will just never dip below 90% thanks to this trait, Mango Pies, the Regeneration Boon and Backpack Regenerator.
Alchemy Grandmaster [HGH or Cleaning Formula 409]: If you are using Elixir C, go with HGH. This will let you give yourself 6+ stacks of Might by using your toss elixir and elixir usage skills on yourself. If you're using the Elixir Gun, the utility from HGH goes down a lot so I'd use Cleaning Formula 409 instead, which will make your Elixir B work like a poor man's Elixir C in addition to its existing effect. I personally don't use Auto Immune Response because it doesn't synergize particularly well with my strategy when I hit 25% HP--typically I get shrunken by Elixir S, go invulnerable, and then immediately use my Med Kit to heal back up to full and my Elixir C to clear all my conditions anyway, so it doesn't have very much time to get use. However, it can save you if you are being bursted with conditions in WvW--but I'd still stick with one of the other two traits.
--- Strategy / Rotations ---
PVE (Easy): Most PVE content against typical trash enemies does not require any complicated strategies. Your typical rotation will go like this
1) Round up as many enemies as possible with the bomb kit/rifle, dropping bombs while pulling them together
2) Drop a Fire Bomb and activate as many Blast Finishers with it as you have equipped to grant many stacks of Area Might
3) After your blast finishers immediately swap to the rifle and jump shot (5) at your location for the Fire Aura combo, then swap back to the Bomb Kit and PBAOE everything to death.
Challenging PVE/WvW: Challenging content is where this build really shines, and where a lot of the trait/skill/gear choices matter. Here, you don't want to just stand and fight. Use the same rotation as above with the following changes:
Dodging: Dodge constantly. If you have energy, you should probably be dodging. Of course, save your dodge if you happen to know your enemy has a strong ability you'll need to save energy for. Dodging doesn't even really hit your DPS or healing too badly, as you automatically have a minor trait to drop a bomb on dodge--which will almost always hit your pursuing opponent.
Kiting: For particularly difficult content, you'll want to kite constantly too, often by circle strafing around an LOS-blocking obstacle. Ranged mobs and players are absolutely shut down by this tactic as they will be constantly faced with the "Obstructed!" message, but they will keep taking the ever-so-slightly delayed damage from your constantly dropping bombs. No matter what they do they are going to be doing reduced ranged DPS to you, but you will keep up damage on them, while healing constantly from all your stacked regeneration. This kiting tactic will let you solo group events, champions, supply camps, and multiple enemy players--if used correctly.
--- Summary Strengths / Weaknesses ---
Strengths: Very high survivability, very high mobility, high support, good condition removal, good control, decent damage, effectiveness increases significantly with player skill. Playstyle is extremely disorienting for most enemy players and navigating your field of bombs will force them to make decisions that will waste their time, giving you the advantage
Weaknesses: Susceptible to stun-locking / control in PVP and to repeated condition stacking. Although this build will rock most PVE content and most PVP opponents, players with heavy stun/daze builds or who are able to stack conditions quickly can get the best of you do to your fairly low health. You will want support or distractions for these sorts of enemies. Damage is not intended to be bursty so if you need to kill something quickly, short of the Big Ol' Bomb, you typically will be forced to win by attrition.