I tried him at around level 25-30 today and he still rocked the hell out of me. Mastered the previous elite dungeon pretty easily.
Baigan -is- still a progression check. Just not a ridiculously insurmountable one now.
As the HP values are ~10k/20k/10k, you need to be able to deal 40k worth of damage, with two bursts - one to zerg down one of the arms ASAP (they hurt) and another at the end to kill him before he regenerates arms. Essentially target one arm, kill it, target body, count all the damage done to it (pause if you have to), and stop at ~17k, blow up other arm, blow up body. You also need to be able to tank the damage that he outputs in the meantime.
Shiva is pretty amazing here. So is Blizzard Strike as it doesn't trigger Reflect.
Gear:
Offense - You should be swimming in Kunais (I had 3 of them maxed out 1*++ and they out-stat everything else I have in IV worlds aside from my gacha Mage Masher IV) as they drop from mobs in IV Elite.
Defense - Had a bunch of Mythril IVs from Armor Daily
Rydia - Should have a maxed out 4* rod (Elite mastery) and Black Cowl by now
I was in the same boat as KojiKnight - bashing head against him pre-nerf. Got as far as doing 30k damage to the body and then swapping to the other arm when I ran out of abilities - my plan was to farm another rank of Shiva and load up on even more Blizzard Strikes, then the nerf hit and he went down first try lol.