The solution for Agrail is where you run around the islands, right? If that's the case, it's not a mission, but rather a gift, especially compared to the other Agrail missions. You run around, gather troops – all Inferno creatures join you, you eliminate everything that moves, and that's basically it until you reach the druid.
And to be honest, completing it without losses isn't really critical. There seem to be dwellings there, and no one is rushing you – there are no other players, just neutrals, so if you have the patience, you can gather even more troops than you might lose.