Sniper

How to unlock: The Sniper is unlocked after beating the game for the first time. He is still unlockable if you've won on Drizzle (Easiest) difficulty.

The Sniper is the ultimate boss killer. A perfect reload and a fully charge Steady Aim, along with Spotter: SCAN, can one shot many bosses. Try to stand in a preferable position where you can charge Steady Aim for as long as possible.

Tactics
A well timed reload can increase damage output incredibly.