Collar of Subordination is an UPGRADE.
For this card to be played there has to be a creature on the board.
Collar of Subordination can be played on friendly or enemy creatures.
When Collar of Subordination is attached to a creature, that creature gains the constant ability: You control this creature.
When the creature that Collar of Subordination is attached to leaves play for any reason, Collar of Subordination goes to its' owners discard pile.