As long as Thundering Mightmare is paired with another creature, each of those creatures has “Whenever an opponent casts a spell, put a +1/+1 counter on this creature.”
Near Mint - $0.40
Lightly Played - $0.30
Moderately Played - $0.30
Heavily Played - $0.30
Damaged - $0.20
Near Mint Spanish - $0.40
Lightly Played Spanish - $0.30
Moderately Played Spanish - $0.30
Heavily Played Spanish - $0.30
Damaged Spanish - $0.20