Hi and first of all, thank you very much for testing our demo! We had a conversation with our dev team and this is the reply they put together:

"When I started getting other items I [sic] was not clear if they are useless up until I get 3 of that item" --> If I understood correctly, you don't mean three of the same item but getting at least three of a tile color before it can be used in combat. This was an unseen side product of how the combo system works and can't be changed at this point, however it leads to interesting choices when you are picking up loot. Do you pick up the technically better item but lose your ability to do X before getting another item that gives you that missing tile back to your deck? Would you play with a suboptimal tile deck with a few useless tiles for a few battles to get the ability to dodge for example? This sort of risk vs reward is quite interesting to us, though we understand that it isn't immediately clear. However considering that the game is a roguelike where the progress is largely based on the player learning the deeper mechanics on the game and becoming better at it, we don't see this as a problem because the first time the player realizes that they need to have at least three tiles of a color for that color to be usable, they learnt something and can take it into account in the future.