Equip the Blade Armor and Ultimate Buster part. Fire the Ice Weapon and Mach-Dash up. You will fire icicles and one will hit Turtloid in the head, freezing him and causing heavy damage. The fully-charged ice weapon is Turtloid's only weakness; the Ultimate Buster, which fires all fully-charged shots, makes this a lot easier. if you do not have it, use Quick-Charge instead.