Sludge Strider is a uncommon Artifact Creature — Insect card from Conflux (CON), collector number 126. Current market price: $0.17 (foil $0.25), TCGplayer market prices via Scryfall.
Whenever another artifact you control enters or leaves the battlefield, you may pay {1}. If you do, target player loses 1 life and you gain 1 life.