Enchantment
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This destroys creatures with mana value exactly equal to the appropriate number, not equal to or less than that number.
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.
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.
(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.)