Hello

Some ennemies returns in the staging area after their attack (wargs, or with some shadow cards). If you defend with grimbeorn, can you attack them with his special ability before they run away ? In other words, does the ability trigger during the attack (at the very end), or just after ?

Grimbeorn's ability does not care where the enemy is during the counterattack (engaged with Grimbeorn's player, another player, in the staging area), the only way to elude its attack is being immune to player card effects. If you had a non immune enemy attacking you from the staging area Grimbeorn would still be able to defend and counterattack it.

You can see it like that, the enemy had to "reach" Grimbeorn for a moment to attack it, so in that moment it's in range of Grimbeorn attacks.

Hum, ok, that's great. Thank you