
Black creatures you control have wither. (They deal damage to creatures in the form of -1/-1 counters.)
Corrosive Mentor has 1 printing, first in Shadowmoor (2008). EDHREC ranks it #10,417 among Commander cards. It appears most in Auntie Ool, Cursewretch decks (1,972 on EDHREC).
Deck counts from EDHREC.
Cards that show up in the same decks on EDHREC.