507.2 Attach to [Type]
507.2a When you play the card, you must pick a target card of the appropriate type as the first extra cost. When the attaching card resolves, it enters play attached to the target card.
507.2b If the attaching card is put into play by something that does not specify a target for it, you must pick a target card as the attaching card enters play.
507.2c If there is no valid target card to pick or the attaching card’s target is no longer in play when the attaching card tries to enter play, put the attaching card into its owner's discard pile instead. If it was already in the discard pile, it just stays there.
507.2d If the attaching card is put into play at the same time as another card, the other card can be selected as a target for the attaching card.
507.2e If the target card stops being the appropriate type, destroy the attaching card immediately.