Overloading Hydragon

Flying, trample, poisontouch
—At the beginning of each upkeep, double the
number of +1/+1 counters one Overloading
Hydragon, if it has none, put a +1/+1 counter
on it. If it has 20 or more +1/+1 counters, you
lose the game.
—Whenever Overloading Hydragon is dealt
damage, you may remove that many +1/+1
counters from it, put that many -1/-1 counters
on each creature blocking or blocked by it.