The egg sac

this creature enters the battlefield tapped and
with X*10 +1+1 counters X is its casting cost
this creature does not untap during your untap
step whenever The egg sac dealt damage remove
that many +1+1 counters from the egg sac
creatures your opponent control have whenever
this creature attacks it may deal damage to
the egg sac equal to its power
After {x} turns create X 1/1 colorless toads where
X is the number of +1+1 counters on
the egg sac then sacrifice the egg sac