Blowfly Infestation

Enchantment, 2B (3)
Whenever a creature is put into a graveyard from the battlefield, if it had a -1/-1 counter on it, put a -1/-1 counter on target creature.¹
When the giant Tollek Worldslayer fell, a corruption erupted from his corpse to carry on his name.
Illus. Drew Tucker

Gatherer Card Rulings [Nov 2009]

• 5/1/2008: When Blowfly Infestation's ability resolves, it will put a single -1/-1 counter on the targeted creature. It doesn't matter how many -1/-1 counters were on the creature that went to a graveyard as long as it had at least one on it.
• 5/1/2008: This ability is mandatory. If you're the only player who controls any creatures when this ability triggers, you must target one of them.

Format Legality	Legal in Vintage, Legacy, Extended, MTGO Classic Banned in Standard
Printings (1/10)	Shadowmoor (Uncommon)