Thanks for the comments! Your critique is fair. As I've mentioned elsewhere, the final boss is a bit broken as of now. Unfortunately, I ran out of time (based on my schedule not the event), so I had to release with a number of things not implemented. Cat/Dog/Spirit are lacking additional skills that would make the boss more manageable. At present the Robot form is the only way to efficiently beat the boss (i.e. without grinding), since it has a full skill package. (Spoiler the boss has about 1800hp. If you use skills effectively the robot can put out around 2-300+ points per turn, circa level . The spirit form takes half damage from physical attacks (most attacks), but also deal half damage to physical enemies, so that's why you're seeing such low damage. Without the added skills that would certainly require the grind you mention.)
I debated nerfing the boss in my last passthrough, but I preferred the challenging version when robot, and the broken other forms combat for initial release. Perhaps this was the wrong choice. However, I completely understand how this is extremely frustrating when you try to play other ways (which you should be able to).
I do plan to patch in the additional skills and maybe balance the boss a bit more after the event.
As for the items issue, I'm not sure what's going on there. Did you play in Browser or download? I can't replicate the issue, though from other comments, it seems to be an issue with browser play, so I'm looking into it. They should work!
If you want to play a better game from me, I recommend Opal! :D Which is a full game developed over a long time instead of 12 days haha, and much better balanced (though combat is still very challenging, however there is no real way to grind in the game, so it's mostly learning the skill system).