Overall pretty fun! The choice of music make the battle feel so epic.
It's generall not a good idea to have key bind at 5~0 when you also need to control the mouse. And it's a bit confusing when the first two usable spell is at 7 and 8.
Gameplay-wise, I think the game stucks in between a challenging game and a no-brainer game. The player is slightly overpowered, but it's not I would thought a evil boss would be. Like if we make the early unlock-stage shorter, and let the player gain unlimited mana while facing multiple heroes at once, I can see the potential of a really great game. Like you are the bullet hell and grossy kills are everywhere.
Finally, I appreciate the effort on the dedicated lore and voice acting,