Flensermite is a common Creature — Phyrexian Gremlin card from Mirrodin Besieged (MBS), collector number 41. Current market price: $0.27 (foil $2.49), 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.) Lifelink (Damage dealt by this creature also causes you to gain that much life.)