My Engineer build is designed as a staller to keep your enemy busy as long as possible while your team captures points or comes to your aid. This build is only up to date as of Beta Weekend Event #1 from 4/27/12 – 4/29/12.
For my weapon slot I use a Pistol/Shield combination to give myself some condition damage to bother my target while providing the stun and knockback of the shield to keep them away from the capture points. With the recent beta it seems all 1 skills are auto-attacks so Explosive Shot will always be going off and you should be using Dart Volley whenever possible, but timing Static Shot is important. Static Shot blinds and confuses each enemy it hits and it can jump between multiple targets, this is really your best counter on your weapon skills to deal with anyone who comes in melee range. Shield skills like Magnetic Field will be useful to knock a player out of the capture point or to create some distance between them. While Static Shield will be used to put distance between you and your foe, and it can also be used to stun them outside the capture point for a couple seconds.
My Traits are 10 Explosives which gives me the minor trait Reserved Mine Deploy and I choose the major trait Big Grenade Pouch for the extra damage and condition chances. I take 0 points into Firearms. I go 15 points into Inventions; this gives me the minor traits Low Health Response System and Automated Medical Response as for the major trait I pick Extra Supplies for more healing. Next I take 15 points into Alchemy which gives me the minor traits Automated Elixir B and Transmute, while I pick the major trait Backpack Regenerator to add that small health regen while fighting since there are very few times I won’t have a kit equipped. Finally I put 30 points into Tools giving the minor traits Adrenaline Pump, Inertial Converter, and Enduring Damage. When it comes to major traits I picked Adrenal Implant to give me more dodges in combat. Then I go with Crippling Wrenches to stall my enemy chasing me or to give me allies an edge when chasing a fleeing for. The last major trait is where the most versatility comes in depending on group setup and how you plan to play the match. The 3rd major trait I went with was Kit Refinement because every time I would swap what kit I had active it would give me an added boost either some healing or extra damage.
Now let me move on to what gives this build its ability to stall the enemy so well, being the use of 4 different kits. The healing skill I go with is the Med Kit. The Med kit not only gives you multiple bandages for some extra healing as you run around and the Stim Brew to put some distance between your foes or move to the next point faster. The tool belt skill Bandage Self is a very short cooldown and heals for a good amount. This moves me onto my next utility skill which is the Tool Kit. This skill may be risky at times because you give up your ranged attacks for fighting in melee range, but being able to time a Magnet skill followed by a quick Pry Bar to knock someone over an edge or just to interrupt your foes skill rotation is extremely useful. My next skill is Elixir Gun and has some of the more limited uses when in combat with multiple enemies. The toolbelt skill Healing Mist is great to use when you’re in combat or have allies around you who could use some extra healing, the same can be said about Super Elixir. Elixir F is useful for kiting and Elixir Spray is more condition damage. The trick to the Elixir Gun is to use Acid Bomb as an escape tool to blast yourself backwards to put some distance between you and your foes. Finally we can move to the last utility skill which is the Grenade Kit. The Grenade Kit is going to be the most offensive kit for you to use. You will want to make sure you time your skills to anticipate your foes movements. The only skill you will have to wait and properly time is the Freeze Grenade to chill your foes.
The idea is swap between kits as they are needed but if you are forced onto the capture point whatever you do, do not abandon it! If you are surrounded by enemies the area of effect abilities of the Grenade Kit will allow you to dish out some decent numbers and if things do start to go poorly that is what your elite skill if for. My elite skill choice is the Supply Crate, not only does this stun when it lands, but it bring in some bandage packs to add to healing but the turret damage is another deterrent to get the enemies to fall back momentarily.
I did not get a chance to play with the extra gear and runes much during the BWE but I can say I only added +5% damage to my weapons and kept the default armor the Engineer gets and things were just fine.