Goblin Plate Mail is a common Artifact — Equipment card from The Hobbit (HOB), collector number 157. Current market price: $0.14 (foil $0.28), TCGplayer market prices via Scryfall.
When this Equipment enters, amass Goblins 1, then attach this Equipment to the amassed Army. (To amass Goblins 1, put a +1/+1 counter on an Army you control. It's also a Goblin. If you don't control an Army, create a 0/0 black Goblin Army creature token first.) Equipped creature gets +1/+0 and has menace. Equip {4}