Contagion Clasp is a uncommon Artifact card from Duel Decks: Elspeth vs. Tezzeret (DDF), collector number 63. Current market price: $0.58, TCGplayer market prices via Scryfall.
When this artifact enters, put a -1/-1 counter on target creature. {4}, {T}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)