I am in celestia and i am lvl 49 in grotto. I need only 10 000 more xp, but the optio guy is pretty hard and my friends that are strong enough to withstand such strong bosses are never online.
You can wait outside the boss' lair until someone else with the quest enters. Or... You can go to the Celestia commons and ask around; just mark your spot by his lair, and if someone can help you, have them port to you at the Grotto. Or... Fight him multiple times and develop a strategy; use your minion, put in more balanceblades, use hydra, etc. After a couple of fights, you should have a pretty good idea of what he casts. What you should always do: kill his minion first!!
