The merchant in your castle sells everything: food, first aid kits, and weapons, but her prices are slightly higher than those of the merchant you will kill.
As for Tetris, it will be easier when the next update for this bonus branch comes out.
I don't understand your indignation; the game isn't difficult and can be completed in 5-6 hours.
In addition, I deliberately simplified it and added difficulty levels. And so you don't have to grind for too long, you can buy the Extended, Deluxe, or Cursed versions. The game is completely free, but as the author, I want to be rewarded for my work, so I added various paid versions of the game with bonus content.