Viola, Tainted Biomantress

Shroud
Whenever you cast a spell, if there are 50 or
more +1/+1 counters on creatures you control,
you win the game.
Whenever one or more +1/+1 counters would
be put on a green or blue creature you control,
that many plus X are put on it instead where X
is the number of permanents you control with
counters on them.