Gandalf, Goblins' Bane

An adventurer card is a permanent card in every zone except the stack, as well as while on the stack if not cast as an Adventure. Ignore its alternative characteristics in those cases. For example, while it's in your graveyard, Bilbo, Luckwearer is a blue creature card whose mana value is 2. It can't be put into your hand by the effect of Speak Secrets ("Mill four cards, then put an instant or sorcery card from among them into your hand.").

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.

Casting a card as an Adventure isn't casting it for an alternative cost. Effects that allow you to cast a spell for an alternative cost or without paying its mana cost may allow you to apply those to the Adventure.