Tarast, the Ozolith's Storm

Whenever you cast an instant on someone
else's turn put a +1/+1 counter on Tarast.
{t} {u/r}{u/r}{u/r}: create X 1/1 Blue and Red Elemental Creature tokens with "when this creature enters the battlefield, mutate it
with target creature" where X is the number
of counters on Tarast.