Let's go gambling

At the beginning of your turn, roll a D20.
1 | place two -1/-1 counters on a creature you control.
2-10 | place one -1/-1 counter on a creature you
control.
11-19 | place one +1/+1 counter on a creature you
control.
20 | place two +1/+1 counter on a creature you
control.

"Ah dang it."