The engineer is often underestimated in Team Fortress 2. His shotgun can be deadly, and the pistol can finish off an enemy at range, or discourage people from out-ranging your sentry. Now the engineer has a lot of fancy tools like mini sentries, the Frontier Justice shotgun (which deals extra damage for every kill your sentry got when someone destroys it), and The Wrangler (which causes your sentry to fire where you want it to). But all of those tools have big downsides, with mini sentries you can never have a max-level sentry, they setup fast and cheap though, so only use them when you know you’ll be moving around your sentry a lot or it’ll be destroyed a lot. The Frontier Justice shotgun only has half the ammo capacity of the regular shotgun, this is fine when you get the extra damage from crits if you destroy your sentry (or someone else does), but otherwise very limiting. The wrangler turns your sentry into (even more of) a killing machine, but it loses it’s auto-aim functionality.
While all of the Engineer’s unlocks have their place, I’ll only be talking about the regular old Engineer, a shotgun, pistol, and wrench. It’s his most versatile loadout, the others have more specialized roles that I can’t get into today. I recommend the basic loadout for almost any situation anyway, and you’ll see why as I explain how I generally go about playing the Engineer.
Regardless of the map, your first move should generally be to place a teleporter entrance just outside of the spawn, now in most maps you should just drop it and run for the next ammo box on your way to the front line, but if the map you’re on is a bit conservative with ammo boxes, you’ll have to run back into the spawn for the resupply cabinet (assuming one exists, as they do on most maps). Now on your way to wherever the enemies are going to be you’ll want to drop your teleporter exit somewhere discrete, but not too far from the action, preferably somewhere an enemy might be likely to run right by without noticing it. Don’t bother to stop and hit it with your wrench, just locate the nearest source of ammo and get in the fight with your team, put a sentry down in a convenient place, I’m not going to go over sentry placement since it varies with the map, but you want to make sure the sentry’s range (indicated by the colored sphere around you) is such that it will either cover an objective, or surprise enemies, also make sure it won’t be easy for someone to hide around a corner, or stand out of range while they dispatch your sentry, since those are the most common ways of removing them with as little risk as possible.
After your sentry is in place, find another ammo box if it’s safe to do so, or defend the sentry with your shotgun if enemies are around. If it’s safe, but your sentry will be vulnerable if you go for ammo, hit it with your wrench, this will speed up the build time, and allow you to go for ammo without leaving your poor sentry defenseless. Now you have to make a choice, if this sentry is destined to be destroyed (easily) you might want to leave it as a level 1, and just throw down another when that happens, a level 1 sentry in a surprising location can actually be fairly effective, keep in mind the level 1 sentry is smaller, and makes less noise than it’s upgraded counterparts, so it might actually live LONGER, and rack up a few more kills than if you upgrade it. A low-rank sentry in a subtle spot can create quite a bit of confusion. However, if you feel it would be better served as area denial upgrading your sentry to it’s highest level will at first get you a couple easy kills, but eventually the enemy will just choose to avoid it, and your sentry will effectively funnel the enemy into whatever other paths are available to them. If they can’t do this, be warned, they will aggressively attack your sentry until it’s destroyed, with a level 3 sentry, and your shotgun though, you can hold that ground for quite a while. Moving your sentry should be a last resort, especially if it’s upgraded, it is a risky maneuver that could end up with both you and the sentry dead.
Demo men can be a nuisance, when you see that first sticky shot at your sentry, you have two options, if you have the aim and speed, you can actually shoot the stickies as they land, destroying them, and minimizing the damage to your sentry, it takes 3 stickies to destroy a level 3 sentry (and two to kill you), this route isn’t recommended, it’s annoying to the demo man, but unless you have teammates around, he’s just going to keep doing it. The best option, option two, is actually to rush the demo man, and pop him a couple times point blank with your shotgun. Stickies aren’t very effective in close quarters combat, and the demo man is unlikely to switch to his grenades (if he does, keep in mind they give him the upper hand here). A demo man attack is a worst case scenario for an engineer, the demo man will always be able to damage, and destroy your sentry with little to no danger to himself assuming he knows where it is, so it’s up to you to defend your sentry from this vicious intruder.
Spies are often seen as the hard counter to the engineer simply because they have a weapon that disables his buildings, but this isn’t actually true, the spy is very ineffective against engineers. Just don’t hug your sentry looking only one way while you repeatedly hit it with your wrench, and you’ll be fine. Shoot the spy, then remove his sappers. One of the spy’s roles is to get behind enemy lines, and capture points when the enemy has pushed forward, this is actually why he has the sapper, if the engineer leaves his gun unattended, but covering the objective, the spy needs to be able to disable that gun before taking the objective. There are many strategies for identifying the spy, and it’s even easier when you’re defending a specific location, I won’t go into how to identify the spy in this article though, just remember, shoot the spy, THEN hit the sapped buildings with your wrench, otherwise he’ll just stab you when you go to repair your buildings.
Remember that the most effective building you have is the teleporter, not your sentry, always keep a teleporter up and available to bring your teammates to the front lines, often times the teleporter will bring such a steady flow of teammates that they alone will keep enemies from destroying it. The teleporter will also allow your team to more easily overwhelm the enemy, the sentry won’t.
Dispensers are great, but place it where teammate’s are going to need healing, rather than where you need metal, there are plenty of ammo crates in most maps, and they should provide you enough metal to build and upgrade your gear, the dispenser should only be used for metal when they are inadequate, since in most cases it will be faster just to run and grab some metal (using your shotgun for defense). Teammates will greatly appreciate an upgraded dispenser in the right place. (Especially in arena matches)
Many engineers believe they are defenseless, but using your shotgun, you can easily be a threat (without your sentry even) to any class, so don’t just cower in a corner if you get attacked, SHOOT BACK! (seems obvious, but I’ve seen this behavior a lot, especially in new engineers, they just give up if they don’t have a sentry). Defend your sentry like a mother bear defending her cubs though, don’t even let anyone NEAR it, falling back to the sentry for backup only when you think you won’t be able to kill the enemy(s) attacking, this is counter-intuitive, but will greatly increase the lifespan of your sentry (so long as you know when to retreat).
One last tip, use your pistol excessively, Valve gave the engineer 200 backup rounds for a reason (the scout has far less for his identical pistol). The pistol is capable of dealing significant damage at a farther range than shotgun, anytime someone is out of ideal range of your shotgun, use your pistol.