Hint - Quick Level Up
Go to Chapter 4-3 "Red Water" first send one character to kill the necos. make sure not to kill the beast master. Send Adell or someone that can throw atleast 5-6 spaces to the geopanel in the top screen and also send the person you want to level and wait in the top right where the geopanel is.
After killing all the necos, keep ending turns until you are satisfied. I recommend if the character is lvl 50, make the beast master around lvl 140, NOTE: Good Equipment. Make Adell destroy the geopanel and make him stand where the geopanel was. Then move the character you want to level stand next to him and make Adell lift that person. MAKE SURE TO END TURN.
Then Adell throws the character to the other side where the beast master is and then move behind the beast master. If you are a swords character and the beastmaster's weakness is wind then use hurricane slash. Or other character's with elemental attacks. Do not attack with weapons and make sure to use specials like blade rush.
Even if the level differencial is large your chance is at least 80% behind him. If you didn't kill him make sure to have other characters that is weaker than him to lure the beast master and try again. I kill a level 2000 beast master with Rozalin lvl 130 strongest gun and full equip with eyewears.