Extreme fluctuation

Enchant creature
Static abilities of enchanted creature are
undulated. On the owner of the creature's
upkeep, they flip a coin. If they win the flip, put
a +1/+1 counter on enchanted creature. If they
lose, put a -1/-1 counter on it instead.
"The power levels were insane! We weren't sure
whether it would explode or just spontaneously
combust!"
Recorded 07/01/4560, Titled "Incident-022"