your opponent Special Summons, in Attack Position, as many monsters as possible from their hand, Deck, and/or Graveyard with the same name as that monster, also, the ATK of the targeted monster and those Special Summoned monster(s) become 0 and place 1 Cubic Counter on each
Rhystic Study Commander is a multiplayer format where it is usually played by at least four players, so a full turn with this enchantment out would get you at least three cards
The Lanterns will let you cast anything you want to find, from a Maelstrom Wanderer, which will let you attack with all your Sanced tokens, to Geth, Lord of the Vault, which will let you steal all your opponents goodies from the graveyards that have grown large over the course of the long game
Then River Song deals damage to that player equal to its power