It is actually possible to beat Chupon. He has 50,305 HP, so, if you level the hell out of Gogo and upgrate his/her/its attack every chance you get, give it the offering and genji glove combo, it should do 9999 damage each attack (for a total of 39,996)... If you're lucky, choupon won't use sneeze and, since gogo only has "fight", it'll use the attack again, killing choupon and giving you an elixer...

I'm sure there's easier ways than this to get elixers, but you did ask how to beat Chupon... You could do this with any other character, but you don't have 100% chance of your character using fight.