Powder Keg

Oracle Text

At the beginning of your upkeep, you may put a fuse counter on Powder Keg.

T, Sacrifice Powder Keg: Destroy each artifact and creature with converted mana cost equal to the number of fuse counters on Powder Keg.

Card Rulings

10/4/2004 Only destroys artifacts and creatures with exactly the specified cost. It does not mean “less than or equal to”.
10/4/2004 Putting on a counter is optional. If you forget, you can’t go back later even if it is something you usually do.