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!!