Catastrophic Storm

Catastrophic Storm deals 1 damage to each nonlegendary creature at the beginning of your
upkeep.
At the beginning of your upkeep, put a Tar
counter on Catastrophic Storm.
Catastrophic Storm deals 1 additional damage
for each Tar counter on it until the total damage
to one permanent equals X. Once X is met,
remove all Tar counters from Catastrophic
Storm.
Cast only if you control a commander.