Great game. I really like the combat, it is kinda challenging at first, but after 30 minutes it was really smooth.
Some things I would suggest tho:
1. Yeah the mummy is by far the hardest enemy, but the thing that bothered me the the most is, that his first punch is random. It is either a short jab or the slower punch and the timing for these is different. Either let him attack always in one combination or show it what comes first. This could be for example that he always attacks with the left hand first and this one is either in front or back.
2. Even tho the minimalistic controls are nice, I would use A and S for choices and D for dialog. I always feared to miss click with the potions because I had to press A only one time. It would just avoid any annoying errors.
3. Maybe add an undo button for the Upgrades, again to avoid errors. (Of course only for the upgrades purchased in the current shopping session)
4. Did you clarify what speed even does? Is it cooldown reduction for actions or the speed of the actual animation. I always felt better having some points in speed, but couldn´t quite pinpoint it.
But all in all the game is really well done for a demo and I look forward to more levels and enemies.