Currently having no problem soloing the Expert modes for this event on auto ability, however it is harder than Sandaphon was so if you dont have a good water team you would definitely want to have some dispels / afflict shields in your group makeup.

Party makeup of Siegfried for soul (using D'Arts Sniper shot debuff for extra skill), Poseiden, Gabriel, Nike and Sol - using Jormungdar for my Eidolon, 33k ATK party.