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!

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Engineer