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 - $1.20
Lightly Played - $1.00
Moderately Played - $0.90
Heavily Played - $0.70
Damaged - $0.60
Near Mint Spanish - $1.20
Lightly Played Spanish - $1.00
Moderately Played Spanish - $0.90
Heavily Played Spanish - $0.70
Damaged Spanish - $0.60