I beat him last night and found a pretty easy way myself: Silence. Since pretty much all of his powerful attacks are spells, just silence him and the battles quite simple, all he does 3 physical attacks each round that dont hit that hard, and the scripted maelstroms that knock 2 members down to 1%. If you want a pretty sure bet win and one of these hit your healer you can give her a high potion, otherwise its hard to lose long as your silence lands.
Plus silence has a higher rate then the paralyze strategy. About 40-50% i think, vs 10-30% on most paralyze. And you can craft silence, then it on tons of characters, where as paralyze is only available on mainly weaker characters except Cyans whos decent.
Youll still want poison to deal with his massive hp pool, but otherwise yea silence, and even if you have no poison so it takes ages to take him down, still possible with silence high proc chance and 2-4 turn duration.
I think blind should also work if your having trouble with the phys attacks, tho didnt bother myself.