First Boss Divine Beast Dran
Ok so for this boss the primary thing you'll want to keep in mind is don't prolong the fight and try to stick around the outsides of the room. He destroys the floor a little bit each time you let a fireball hit it so don't spend too much time dodging his attacks without counters. With that in mind; don't worry, this guy is a total cake walk.
All you need to do is shoot him with Xiao when he goes up into the air and he will land to scratch his ear for about 5 seconds. You'll wanna switch to Toan and deliver an attack while he is scratching his ear. If you attack with Xiao a second time while he is doing this he'll charge you which is pretty hard to dodge
Honestly, that's really all there is to this boss. Like I said, fret not he is as easy as can be. If you're having trouble with him try grinding Xiao or Toan's weapon up a little bit in the early floors of the mine.