Flying
Each creature you control that has an Adventure enters the battlefield with an additional +1/+1 counter on it. (It doesn't need to have gone on the adventure first.)
A creature with an Adventure you control that would enter the battlefield with no +1/+1 counters on it enters with one +1/+1 counter on it.
An effect may refer to a card, spell, or permanent that “has an Adventure.” This refers to a card, spell, or permanent that has an adventurer card's set of alternative characteristics, even if they're not being used and even if that card was never cast as an Adventure.
If an effect refers to a creature card, creature spell, or creature that has an Adventure, it won't find an instant or sorcery spell on the stack that's been cast as an Adventure.