Sheylana, Forbidden Ascetic

Sheylana, Forbidden Ascetic enters the battlefield with three +1/+1 counters on it.
Whenever your opponent casts a spell, flip a coin. If you win the flip, put a +1/+1 counter on Sheylana, Forbidden Ascetic.
Remove two +1/+1 counters from Sheylana: Target creature becomes a 2/2 black Chimera creature token with deathtouch under your control.