Hello Deimus can i ask you how to kill giant slime?
Choosing not to fight the slime postpones the fight, so you have a chance to level up more.
Buy and equip the arcane ring from the accessory shop. It makes your magic stronger.
Buy the electric spell. It does huge damage to water-type enemies.
Create magic potions to restore your magic. You can use these potions during battle.
Focus your attacks on the boss slime by selecting him before casting a magic spell.