Rakdos Riteknife is a rare Artifact — Equipment card from Dissension (DIS), collector number 164. Current market price: $0.37 (foil $2.50), TCGplayer market prices via Scryfall.
Equipped creature gets +1/+0 for each blood counter on this Equipment and has "{T}, Sacrifice a creature: Put a blood counter on Rakdos Riteknife." {B}{R}, Sacrifice this Equipment: Target player sacrifices a permanent of their choice for each blood counter on this Equipment. Equip {2}