Kemba's Banner is a rare Artifact — Equipment card from Phyrexia: All Will Be One Commander (ONC), collector number 45. Current market price: $0.34, TCGplayer market prices via Scryfall.
For Mirrodin! (When this Equipment enters, create a 2/2 red Rebel creature token, then attach this to it.) Equipped creature gets +1/+1 for each creature you control. Equip {2}{W}