Drain an enemy's health to heal yourself. Drain is the Voodoo school's sustain tool and the most self-sufficient spell in the game. The exchange is straightforward, the 25 second cooldown is the shortest in the school, and it keeps you alive through encounters that would otherwise require a utility item or a teammate.
Strategy
Use it proactively during sustained fights rather than as a panic button. Against enemies that need to be in melee range anyway, Drain can cover the incoming damage before it stacks. Mark Ace from the Revolver makes the target take +15% damage, which helps whatever you fire after the drain.
Strengths
Direct health exchange makes it reliable sustain in any situation
Short cooldown for a healing spell
Works solo - no allies or positioning required
Weaknesses
Requires an enemy target - useless between fights
The heal is modest late-game without healing upgrades