2/3 of its actions are water normal attacks. The rest are Mega quake, a water attack on 1 target (power 65), and the thunder spell Flash.
Equip the Battle knife from Sundletan's weapons shop to use the IP skill Thunder blast, which deals 1.5x normal damage
IP builds faster the more damage you take relative to your remaining HP, so it fills quickly in this solo battle. Once it fills, unleash Thunder blast.
Water is halved, and the only attack spell Maxim can learn at this point is the water spell Droplet, so spend MP on the recovery spell Strong
Sleep, confusion, paralysis, poison, and freeze magic have no effect, so don't use Drowsy even if you know it