Fludge, Gunk Guardian is a rare Legendary Creature — Slug Ooze card from Mystery Booster 2 (MB2), collector number 593. Current market price: $0.22, TCGplayer market prices via Scryfall.
Whenever Fludge, Gunk Guardian or another Slug, Ooze, Fungus, or Mutant enters the battlefield under your control, each opponent shuffles three Gunk cards into their library. (Gunk is a colorless sorcery card with no mana cost that has cycling {4}.)