303.4f If an Aura is entering the battlefield under a player’s control by any means other than by
resolving as an Aura spell, and the effect putting it onto the battlefield doesn’t specify the object
or player the Aura will enchant, that player chooses what it will enchant as the Aura enters the
battlefield. The player must choose a legal object or player according to the Aura’s enchant
ability and any other applicable effects
(12/15/23)

Abilities are gained and lost in layer 6 and go by order of timestamp (usually) (see 613.3, 613.1f)

613.7e An Aura, Equipment, or Fortification receives a new timestamp each time it becomes
attached to an object or player