Great concept, though this version of the game needs a fair bit of polish. Lots of bugs seem to exist and buying upgrades confused me for a bit.
I'll start with the buying upgrades, you have to click on the word buy on the lower right of each icon to buy an upgrade. That second icon in the lower right is NOT the 'buy' button, it's actually your second spell slot. Click on the bottom right word buy to get that too like the others.
One quirk of the game I don't like is as soon as the level loads, the enemy base starts sending monsters at you. This seems a little cheap since the enemy gets a head start while you confirm the start of the level. This isn't good in a game like this where time of of the essence for stacking.
Some squares seem to bug out sometimes. You try to stack a creature on top of the bugged square but acts like the creature on that square didn't exist at all. It seems even though the creature stack graphic exists, it really doesn't. Further more, the bugged square will continue to 'eat' creatures leaving empty graphics as you try to use that bugged square so you have to use twice the amount of creatures.
I passed the 5th level and I don't think it gave me the three stars it was supposed to.
Sometimes the fortress seems invincible to attacks until you summon a creature. (Not the worst bug, lol)
I would like to see an option for half speed or even quarter speed among the speed options.
Unstacking creatures would be a nice option as sometimes you accidentally click the stack button too early.
Spell cool downs seem a bit long considering you only have the option of two spells. But that's just an opinion.
This game will be much better once the bug square issue is resolved. Also getting cheated out of stars really hurts.