Because exiling a card with foretell from your hand is a special action, you can do so any time you have priority during your turn, including in response to spells and abilities. Once you announce you’re taking the action, no other player can respond by trying to remove the card from your hand.

Casting a foretold card from exile follows the timing rules for that card. If you foretell an instant card, you can cast it as soon as the next player’s turn. In most cases, if you foretell a card that isn’t an instant (or doesn’t have flash), you’ll have to wait until your next turn to cast it.

A permanent card is an artifact, creature, enchantment, land, or planeswalker card.

If the mana cost of a card in your graveyard includes {X}, X is considered to be 0.

If you return an Aura this way, you choose what the Aura will enchant just before it enters the battlefield. An Aura returning to the battlefield this way doesn’t target the player or permanent it will enchant, so permanents or players with hexproof may be chosen; however, the chosen recipient must be able to legally be enchanted by the Aura, so a player or permanent with protection from one of the Aura’s qualities can’t be chosen this way. If there’s nothing legal for the Aura to enchant, it stays in the graveyard.

If you’re casting a foretold card from exile for its foretell cost, you can’t choose to cast it for any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the card has any mandatory additional costs, those must be paid to cast the spell.