This boss can be a bit of a doozie because it's spread out over 3 battles throughout the dungeon.
The first battle is a warm up against a bulky technical attacker. Battle 2 has you try to guess what rock the Basarios is disguised as.
The last battle starts at 10:27 for anyone that only wants to see that part
Then you get to battle 3 and here's the real fight. You need to break open his stomach to do any real damage. I recommend only using 2 barrel bombs and try to get some stomach damage in with team attacks.
In his base form his damage is honestly pathetic and the only real thing to watch out for is poison gas.
HOWEVER his enraged form is a different story with power attacks that can do massive damage and if you fail a clash you may be one shot and after a while it will unleash its anger and nuke the party with fire which is very dangerous.
