Mushroom Mischief

When Mushroom Mischief enters, target artifact gains X rust counters. Whenever an artifact leaves the battlefield, if it had any rust counters, create that many 1/1 saproling creature token.

(Artifact are sacrificed at the end of their owner's end step if any rust counters remain on that permenant. Players may remove rust counters
by paying 1 mana or 1 life per counter.)