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 - $3.90
Lightly Played Foil - $3.70
Moderately Played Foil - $3.50
Heavily Played Foil - $3.10
Damaged Foil - $2.60
NM-Mint Foil Non English - $3.90
Lightly Played Foil Non English - $3.70
Moderately Played Foil Non English - $3.50
Heavily Played Foil Non English - $3.10
Damaged Foil Non English - $2.60