as I am fighting him for my second time, I noticed a few things. here they are.
The boss saves up for big spells. at least rank six or up, besides a few other spells he uses as he loses health. Following this, he knows a rank 6 humongofrog.
him and his minions are terrible at critical blocking, but your critical block is slightly lowered. coincidence? maybe not.
he is a sitting duck if alone. he needs his minions for the shields. take out the minions first!
this is what I've noticed. hope it helped for anyone else who reads.