I get it now

Was SUPER confused at first, but once you understand it it's a really nice way to just waste some time. Love the game!

I did it

I don't understand this. You very quickly run out of spaces you can attack that are survivable with the amount of health and xp you have. If I have no healing scrolls, 3 hearts and every possible clickable tile is over 3, what do I do except lose?

No seriously, I feel like I have to be missing something. The farthest I've gotten is level 9 and these are the stats you get as you level:
Level 1 (Starting Level): 5 health 4 xp
Level 2: 5 health 5 xp
Level 3: 6 health 7 xp
Level 4: 6 health 9 xp
Level 5: 7 health 9 xp
Level 6: 7 health 10 xp
Level 7: 8 health 12 xp
Level 8: 8 health 12 xp
Level 9: 9 health 12 xp

As soon as you hit Level 3, your xp to level and regain your health outweighs the amount of health you can actually invest into killing monsters. Even if you are being super conservative and making sure you exhaust all of your hearts between healing so nothing is wasted, I don't see any possible way you can win this beyond getting extremely lucky with the healing scrolls dropping just enough that it outweighs the health deficit. Unless I'm completely missing something, there is absolutely no way beyond random tiles to get more than 1 xp per 1 health you spend...so you just try to clear as many tiles as possible (by killing low level enemies, better to kill 5 rats than 1 slime) and pray to RNGesus? I don't understand it.

Awesome game.