Whenever you cast a blue spell, Gravelgill Duo gets +1/+1 until end of turn. Whenever you cast a black spell, Gravelgill Duo gains fear until end of turn. (It can't be blocked except by artifact creatures and/or black creatures.)
NM-Mint - $0.25
Lightly Played - $0.23
Moderately Played - $0.20
Heavily Played - $0.17
Damaged - $0.13
NM-Mint Non English - $0.25
Lightly Played Non English - $0.23
Moderately Played Non English - $0.20
Heavily Played Non English - $0.17
Damaged Non English - $0.13
Foil Prices
NM-Mint Foil - $0.70
Lightly Played Foil - $0.70
Moderately Played Foil - $0.60
Heavily Played Foil - $0.50
Damaged Foil - $0.40
NM-Mint Foil Non English - $0.70
Lightly Played Foil Non English - $0.70
Moderately Played Foil Non English - $0.60
Heavily Played Foil Non English - $0.50
Damaged Foil Non English - $0.40