Does anyone have any tips on how to beat the boss? I tried but I couldn't beat it with a gem sword.
For both of you, yes you can. First you need to find the 4 chests in the surface (the dark brown squares in the map) with the wood shovel, inside them there will be one talisman piece. With the four pieces, go to the factory and create it with 2 bottles of glue, also, create a couple of potions in the chem lab (they restore all your health). Grab the talisman, the potion and the gem sword and enter the boss cave.
When facing him, grab the talisman and activate it with Z, the boss will be petrified for a short time, attack him and then step back because he will start to move again. Repeat the same thing until you kill him.
I hope you can win him, if you have any doubt just tell me :)