Neat concept ! i like it very much, good controls, and nice music, but most importantly smooth all around implementation.
but i have some comments, adding sound effects and a better graphics and UI would make it 10x better however it's to be expected from a jam game, i think that the tutorial isn't intuitive maybe you could pause the screen while you're playing and then inform the player about what to do mid game, and i feel like the game area is useless simply because you'll be spending most of your time defending the portal which in turn makes you stationary and you only have to move as far as the first health and mana pool reside. otherwise great game.
also i found a bug in the middle spell , the name isn't shown it takes the name of the side spells which is confusing