Thank you for the feedback! I totally agree with the particle effects, something to show off the activation of the spell and some trails and effects coming of the spells would be a lot more satisfying.
The spells only turn invisible and do nothing when there aren't any targets left. The problem with the explosion spell is that you have to do it pretty quickly otherwise the spell resets and counts it as wrong, this is due to the spell timer being the same for each spell and the explosion spell being the longest spell.
I think the idea could work really well in a semi-open world game with selectable spells which you can upgrade and customise yourself. I think learning the spell patterns would be a lot easier in a long game instead of one you spend 3 minutes on .