You only get some special equipments from the extra challenges.
The purple slimes are probably one of the hardest fights, I probably shouldn't have placed them first, also if you picked a cursed ring together with the magic twig at the start... I'm sorry, I did not balance them with that option in mind.
The only tips I can think of in this situation is 1 grinding a few extra levels fighting flame slimes or the plant boss (it respawns in another area) 2 buying other weapons from the kobold merchant and trying them out.