Engineer

Tactics

 * The Engineer can lay mines on-the-go, making them an excellent tool for "kiting" (attacking enemies while you flee to stay out of range of their attacks).
 * don't detonate on contact with walls, although they detonate after 4 bounces (or on contact with an enemy). This means you can bounce them off of walls to hit enemies behind you or from odd angles in a vertical shaft.
 * Thermal Harpoon has incredible range and tracking, easily able to hit enemies far offscreen. This saves the Engineer a lot of travel when only a few enemies remain in hard-to-reach areas.
 * 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.
 * Sometimes laying a mine or two near your 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.
 * If you're quick, you can jump off a ladder/rope and drop a mine before grabbing on again, allowing for safe damage. The same can be done for your.
 * In terms of 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 (item that resets cooldowns) will not give you an instant turret or mine when it's used.
 * 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.

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Engineer