A solid tower defence. Overupgrading is a good and unexpected twist. Spooky vibes, nice sound (both music and fx).
This might be too much nitpicking, but I wish game checked for soul count every frame and updated UI accordingly. For example if im wanna build a tower, I press the gravestone, if I hadn't enough souls to build at the moment it would stay locked untill I reopen same build menu.
Oh nice variaty of enemies. Also good job with animation and auto-targeting. Works like a charm
Solid game, 9/10