Great game! The polish on this is wonderful - the graphics and particle effects are crisp and the sound design is good too (the rising tone as you summon more minions is a satisfying touch)!
Can see this concept being expanded with more hero/enemy types and patterns, and different summons too. Well done!
I liked how the crystal being near enemies means you are incentivised to stay near them - a fun risk/reward element. Sometimes I found the crystal was very difficult to get to, though, and it was best to play passively and draw the enemies away from it - I wonder what it would play like to have mana regenerate if you were inside an enemy's radius?