Pita been using your pack in my game and think its great. I'm hoping that in your next update you would be able to add the levers (which you said you would be happy to do, so that's cool). Pots breaking into pieces, Coins, Hearts, Keys (These 3 just to keep the ui /items in theme with the graphics).
I've made myself using your art a sliding down metal bar door which i think looks pretty cool so i think you should add something like that in as well.
I hope these are suggestions that you would happy to do in future updates. Looking forward to your monster pack!!