Core Prowler is a uncommon Artifact Creature — Phyrexian Horror card from Mirrodin Besieged (MBS), collector number 103. Current market price: $0.64 (foil $5.01), TCGplayer market prices via Scryfall.
Infect (This creature deals damage to creatures in the form of -1/-1 counters and to players in the form of poison counters.) When this creature dies, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)