If Kaya's Ghostform ends up having a different controller than the permanent it enchants due to Claim the Firstborn, Kaya's Ghostform will go to the graveyard as a state-based action for being attached to something it can't enchant (C.R. 702.5a, 704.5m). That's because Kaya's Ghostform says "Enchant creature or planeswalker you control", which means it can enchant only a "creature or planeswalker you control" (C.R. 702.5a, 109.5). Compare Kaya's Ghostform with Brink of Disaster, which can enchant any "creature or land" no matter who controls it (C.R. 303.4, 702.5a).
so "enchant" isn't so much casting it. youre not 'enchanting from hand to the card" - "enchant" then is defined as a card that is attached to another card is "enchant'ed"?
An aura that's attached to an object/player "enchants" that object/player. The "enchant" keyword defines what the aura can enchant, and what the aura spell can target when it is cast. An illegally attached aura, or one that isn't attached at all, is put into its owner's graveyard as a state based action.
702.5 Enchant
702.5a Enchant is a static ability, written “Enchant [object or player].” The enchant ability restricts what an Aura spell can target and what an Aura can enchant.
702.5b For more information about Auras, see rule 303, “Enchantments.”
702.5c If an Aura has multiple instances of enchant, all of them apply. The Aura’s target must follow the restrictions from all the instances of enchant. The Aura can enchant only objects or players that match all of its enchant abilities.
702.5d Auras that can enchant a player can target and be attached to players. Such Auras can’t target permanents and can’t be attached to permanents.
704.5 The state-based actions are as follows:
[...]
704.5m If an Aura is attached to an illegal object or player, or is not attached to an object or player, that Aura is put into its owner’s graveyard.
Enchant is a keyword ability that defines what the Aura can be attached to. The Aura "enchants" the object or player it is attached to.
When you cast the Aura as a spell, it targets, and the target is defined by its Enchant ability. And once it is on the battlefield, it needs to stay attached to something its Enchant ability allows for, otherwise it goes to the graveyard.
303.4. Some enchantments have the subtype "Aura." An Aura enters the battlefield attached to an object or player. What an Aura can be attached to is defined by its enchant keyword ability (see rule 702.5, "Enchant"). Other effects can limit what a permanent can be enchanted by.
303.4a. An Aura spell requires a target, which is defined by its enchant ability.
303.4b. The object or player an Aura is attached to is called enchanted. The Aura is attached to, or "enchants," that object or player.
303.4c. If an Aura is enchanting an illegal object or player as defined by its enchant ability and other applicable effects, the object it was attached to no longer exists, or the player it was attached to has left the game, the Aura is put into its owner's graveyard. (This is a state-based action. See rule 704.)
kaya's ghostform
When opponent claims creature with kaya on it - kaya falls off? Why?
Thanks
EDIT (Jun. 7): Edit rule citation.
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When you cast the Aura as a spell, it targets, and the target is defined by its Enchant ability. And once it is on the battlefield, it needs to stay attached to something its Enchant ability allows for, otherwise it goes to the graveyard.
303.4. Some enchantments have the subtype "Aura." An Aura enters the battlefield attached to an object or player. What an Aura can be attached to is defined by its enchant keyword ability (see rule 702.5, "Enchant"). Other effects can limit what a permanent can be enchanted by.
303.4a. An Aura spell requires a target, which is defined by its enchant ability.
303.4b. The object or player an Aura is attached to is called enchanted. The Aura is attached to, or "enchants," that object or player.
303.4c. If an Aura is enchanting an illegal object or player as defined by its enchant ability and other applicable effects, the object it was attached to no longer exists, or the player it was attached to has left the game, the Aura is put into its owner's graveyard. (This is a state-based action. See rule 704.)