Turn it face up any time for its mana cost if it's a creature card.) If Curator Beastie enters under your control at the same time as one or more colorless creatures, those colorless creatures won't enter with additional +1/+1 counters
The -3 lets you destroy a target creature, and finally, the -6 gives you an emblem that states "whenever you gain life, target opponent loses that much life." Given that this card only costs four mana to cas t, it, like most of Witherbloom, is quite finely balanced and should see plenty of play across Standard and Commander
That said, there are some clear synergies that this sort of design enables that seem worth pointing out
Monstrous Monstrosity is the ability itself while monstrous is the state it becomes after having used monstrosity
I have played (on the draw obviously) Blackmail and had it be better than a Coercion (they had a land I could take!)
My main issue with this card is that the cost of using it feels so high