Merfolk Secretkeeper // Venture Deeper

When casting a spell as an Adventure, use the alternative characteristics and ignore all of the card's normal characteristics. The spell's color, mana cost, mana value, and so on are determined by only those alternative characteristics. If the spell leaves the stack, it immediately resumes using its normal characteristics.

If an object becomes a copy of an object that has an Adventure, the copy also has an Adventure. If it changes zones, it will either cease to exist (if it's a token) or cease to be a copy (if it's a nontoken permanent), and so you won't be able to cast it as an Adventure.

If an effect instructs you to choose a card name, you may choose the alternative Adventure name. Consider only the alternative characteristics to determine whether that is an appropriate name to choose.

If a spell is cast as an Adventure, its controller exiles it instead of putting it into its owner's graveyard as it resolves. For as long as it remains exiled, that player may cast it as a permanent spell. If an Adventure spell leaves the stack in any way other than resolving (most likely by being countered or by failing to resolve because its targets have all become illegal), that card won't be exiled and the spell's controller won't be able to cast it as a permanent later.

If an effect copies an Adventure spell, that copy is exiled as it resolves. It ceases to exist as a state-based action; it's not possible to cast the copy as a permanent.

You must still follow any timing restrictions and permissions for the permanent spell you cast from exile. Normally, you'll be able to cast it only during your main phase while the stack is empty.