Horn of Valhalla // Ysgard's Call

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 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 from exile.

You must still follow any relevant timing rules 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.