Crawl

Play on Easy with one opponent (if you are confident, play against three opponents to speed up the Leveling, you will need to get to level 10 to fight one of three random Bosses).

You can defeat Kourok smacking bomb creature against his face the moment he uses his beam attack. Then his brain shall be exposed to hit it with your weapons or other bomb creature.

When facing Kourok, just wait in thé bottom left or right corner. You will hear a falling sound when a bomb creature drops. Position yourself behind it and wait as long as possible to smack it with your weapon targeting thé Boss. If done right, immediately after another bomb creature will fall which you can use to smack against thé brains of thé Boss.

This will take several attempts as timing is crucial. Equipping items which reduce damage and agility potions you buy during thé game can help to be mobile and fast enough in thé Boss encounter.