Does Baron come in exhausted or can he gank right away?

Baron Nashor enters the battlefield exhausted, and he cannot gank immediately.

Here is the breakdown of why:

1. Exhaustion by Default: According to the rules and RiftJudge FAQ #8856, all units enter the battlefield exhausted unless a specific card effect states otherwise. Baron Nashor’s card text does not contain any effect that allows him to enter the battlefield ready.
2. Exhaustion and Abilities: Because Baron Nashor enters exhausted, he is "spent" as soon as he hits the board.
3. Ganking Requirements: Even if Baron Nashor had the Ganking keyword (which he does not—the card text provided indicates he has passive abilities that protect him and buff friendly units, but Ganking is not listed), Ganking is a modification to a unit's Standard Move. Standard Moves require exhausting the unit as a cost (Rule 144.2). Because Baron Nashor is already exhausted upon entering, he cannot pay the cost to perform a Standard Move (or a Gank move) until he is readied during your next Awaken Phase.

In summary, he arrives exhausted and must wait until your next turn to take any actions that require him to be ready.