In the worst case, I guess you should just go back and get Sabin. You could make it a CESS challenge.
The tentacles got 4000-7000 HP each. How much dammage do you with Bio Blaster?
About 80.
I already went back and got Sabin. I'm just going to finish this challenge as is for now. I might come back later and attempt a CES challenge. I'm In Daryls tomb right now and I'm not certain how to beat Dullahan.