Engineer

Tactics

 * If you're quick, you can jump off a ladder/rope and drop a Mine or Turret before grabbing on again, allowing for safe damage. They will typically fall to the ground below, but not always. This also works off ledges: hop out, drop a mine/turret, then quickly change direction to land back on the ledge. It is possible with no jump or move speed boosts, but much safer with them.


 * Tri-nades don't detonate on contact with walls, although they detonate after 4 bounces (or on contact with an enemy). You can bounce them off of walls to hit enemies behind you or from odd angles in a vertical shaft.
 * Soldier's Syringe will speed up the time between the engineer being able to shoot again.


 * The Engineer does not lose momentum when laying mines, making them an excellent tool for "kiting" (attacking enemies while you flee to stay out of range of their attacks).
 * The detonation is treated as a hit, procing on-hit items.
 * The Spirit artifact can make mines very hard to use. Any fast-moving enemy can trigger a mine, but move past it before the detonation. This can cause an entire field to go off with no damage done. Jump over the enemy so it changes direction on top of the mine; this should provide enough time for detonation.
 * Improperly clustering mines can reduce their effectiveness. An enemy hit by a blast may be knocked past the next mine, causing it to detonate without dealing damage.


 * Has good range and tracking, easily able to hit enemies in hard-to-reach places. This saves the Engineer a lot of travel.
 * Stops all horizontal movement of the Engineer. This is mostly detrimental, requiring time to fire it while remaining safe. The Engineer can jump at any time while using it, so vertical dodging can work well with Hopoo Feathers or Photon Jetpack. It can be useful, too, if performing tricky jumps, by using it to stop you from overshooting a platform. Try it when getting the Spirit Artifact in the Temple.
 * You can safely use in a group of enemies by laying two mines, and jumping while activating the skill. This will give you enough time to resume running at a safe distance.
 * Attack speed affects the time it takes for the harpoons to fire. Stack Soldier's Syringes to reduce the time you're immobile.


 * Their attack speed scales with the engineer's current attack speed, including attack speed modifier items.
 * Turrets can draw monster aggro. They seem to have an aggro priority equal to the player, making them gain the player's aggro if the enemies lose it.
 * Turrets can be stacked with mines to aggro Magma Worms and Wandering Vagrants quite effectively.
 * Sometimes laying a Mine or two near your Turret will redirect monster aggro. This is a great tactic you can use to distract large amounts of mobs, including bosses; this is especially good against Providence, as you can place a turret, stand back and batter him while he hacks away at your turret.
 * They are not invulnerable, although they sometimes seem extremely tough and other times die very quickly. Putting them in a slightly hard-to-reach spot, such as just past a gap in platforms, will allow them to aggro without actually taking damage. Try using them as a meat (metal?) shield, with mines and grenades stunning enemies.
 * Be very careful with elite Overloading monsters, as the Turrets will conduct electricity, increasing the range of the enemy electricity and possibly hitting you in the process (if you've just dropped them, for instance).
 * Items such as Brilliant Behemoth will NOT affect your turrets. They will just continue to fire normal bullets.

Items

 * Any on-hit items are amazing, since the Engineer shoots 3 grenades with his basic attack.
 * Alien Head will generate Turrets, and presumably Mines, faster. However, Gigantic Amethyst (Use Item that resets cooldowns) will not give you an instant turret or mine when it's used. The Wicked Ring does not help produce mines or turrets any faster.
 * Engineer benefits greatly from items that give him additional time in the air. Thermal Harpoons can be fired safely while airborne and staying in the air for a second or two will often cause enemies to clump up beneath you, making for maximum mine efficiency. Don't forget that Mines can be dropped while airborne as well! An effective item for doing this is the Photon Jetpack as you can not only keep airborne longer but also maintain some forward momentum as well.
 * Dynamite Plunger is a fantastic item for the Engineer, especially at low levels, against Magma Worms/Overloading Magma Worms/Cremators (and most other bosses), as they can one-shot most of them with a good pile of dynamite and the right timing.
 * The damaging trails of Fireman's Boots and Burning Witness can work well with mines for kiting.

History
Engineer