Lake-town Mariners

If you cast an adventurer card as an Adventure, use only its alternative characteristics to determine whether it's legal to cast that spell. For example, if you control Gandalf, Party Guest ("At the beginning of combat on your turn, you may cast an instant or sorcery spell with mana value X or less from your hand without paying its mana cost, where X is twice the number of legendary Wizards you control."), you could cast Burglar's Plot from your hand without paying its mana cost (provided you control enough legendary Wizards), but not Bilbo, Luckwearer.

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.

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.