At the beginning of each upkeep, put a strife counter on Crescendo of War. Attacking creatures get +1/+0 for each strife counter on Crescendo of War. Blocking creatures you control get +1/+0 for each strife counter on Crescendo of War.
NM-Mint - $2.80
Lightly Played - $2.70
Moderately Played - $2.60
Heavily Played - $2.30
Damaged - $1.90
NM-Mint Non English - $2.80
Lightly Played Non English - $2.70
Moderately Played Non English - $2.60
Heavily Played Non English - $2.30
Damaged Non English - $1.90