Whenever Thrummingbird deals combat damage to a player, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
NM-Mint Foil - $0.80
Lightly Played Foil - $0.70
Moderately Played Foil - $0.70
Heavily Played Foil - $0.60
Damaged Foil - $0.50
NM-Mint Foil Non English - $0.80
Lightly Played Foil Non English - $0.70
Moderately Played Foil Non English - $0.70
Heavily Played Foil Non English - $0.60
Damaged Foil Non English - $0.50