(I'm back) In order for lv 21 and above to be of some use, I decided to add "Upgrade Cards". This will allow you to choose what you want to improve, but each card has a limit (that's the downside). They will only appear when you raise lv 21 and above.

Underworld Frisk

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Battle system (This is how the battle system might look like)

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Dusttale Sans

Core Frisk

I decided to update the design a little: warp zone (But this may change)

Clover

Health Bar (for monsters) (+ sprites for monsters that I managed to make (3 + hard mode)).

The chances of monsters appearing:

Normal: 80%

Hard mode: 20% (after lvl 10)