Wave of Terror
Cumulative upkeep 
(At the beginning of your upkeep, put an age counter on this permanent, then sacrifice it unless you pay its upkeep cost for each age counter on it.)
At the beginning of your draw step, destroy each creature with mana value equal to the number of age counters on this enchantment. They can't be regenerated.
The sea of fear has endless depths.
Illustrated by Adrian Smith
This printing
Prices
Will not generally kill zero cost creatures because the age counters go on before the ability triggers. If would be possible if something like Power Conduit were removing counters.
If you don't pay the cumulative upkeep, you'll sacrifice Wave of Terror before your draw step begins. It won't destroy any creatures that turn.
This destroys creatures with mana value exactly equal to the appropriate number, not equal to or less than that number.
