User produces sticky balls from their skin that can make crystals grow in what in the ball is stuck to

Pros:
-crystals grow off the target's energy
-user can trap targets
-user can control where crystals grow
-user can control crystal growth
-user can control how the crystals effect targets

Cons:
-user will bleed if too many balls are produced
-user will be able obsessed with crystal formations
-crystals will kill targets quickly
-effects if crystal are random when user isn't in control
-user can't control growth when weak

Weakness: unknown (ideas?)