Ring of Kalonia is a uncommon Artifact — Equipment card from Magic 2013 (M13), collector number 212. Current market price: $0.36 (foil $3.18), TCGplayer market prices via Scryfall.
Equipped creature has trample. (It can deal excess combat damage to the player or planeswalker it's attacking.) At the beginning of your upkeep, put a +1/+1 counter on equipped creature if it's green. Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)