This is more detailed than I thought it would be at first. It's essentially, tower defence; you're attacked by an endless wave of heroes aiming to smash your collection of crystals, and you create monsters to fight back against them; your monsters are confined to the square they're on, but you can upgrade them with points. Points (well, "souls") get generated by your crystals, so you have the normal tower-defence decision to make, of "do I have a whole bunch of quite rubbish monsters", versus "do I have only a couple of monsters but upgrade them continuously until they turn into the Hulk"? And I'm not sure which is actually best here, which is a good sign. The upgrade tree is complex, though; all created monsters start as a blob, and depending on which of their stats you upgrade, they turn into a variety of different monsters, and I never had a very good handle on which collection of upgrades turned my blob into a mega blob, or a skeleton, or a demon. It would be good if there were some sort of on-screen indication of where the next upgrade or upgrades will occur and what they might be, so I can choose to evolve in a different direction without having to try to make notes about what the upgrade tree looks like. One of the upgrade paths even leads to crystals, interestingly, so you can breed more crystals to get more points, thus regaining your power source after the heroes have destroyed some of them. This is a good mechanic, and I liked the ideas behind this game quite a lot. It suffers from the 64px restriction, though; the playfield is bigger than the screen, so you end up scrolling around the battlefield while looking at it through a pinhole, which is pretty annoying. But that doesn't affect the core gameplay much, and I like the core gameplay. Nice work.
Also, since I'm a developer and all, I thought, hahaha, I'll just stop the game in the debugger and give myself 100,000 souls and then I can upgrade everything and win massively. I was rather crestfallen to find out that the hero generation rate is actually tied to the number of souls you've got, so my little hacking adventure lasted about a minute before an unstoppable wave of hero death overwhelmed my monster force faster than I could upgrade them or add reinforcements. Very clever, developers. :-)