At the beginning of each upkeep, count the number of permanents. If the number is odd, until end of turn, red creatures get +1/+1 and whenever a player taps a Mountain for mana, that player adds an additional {R}. If the number is even, until end of turn, red creatures get -1/-1 and if a player taps a Mountain for mana, that Mountain produces colorless mana instead of any other type.
Near Mint - $1.10
Near Mint Non-English - $1.10
Lightly Played - $1.00
Lightly Played Non-English - $1.00
Played - $0.80
Played Non-English - $0.80
Heavily Played - $0.70
Heavily Played Non-English - $0.70
Damaged - $0.60
Damaged Non-English - $0.60