The difficulty goes up every time you level up, isntead of with time or score. Therefore, to score as many points as possible, try not to level up. Turret in one spot and hope you don't catch a lot of pixels.
Nice game, original concept and good execution. Needs some polishing and bug fixes. One bug I noticed is that when you summon something, you can go back to the summon menu and while everything in the game is paused, the summoning timer keeps going so you can summon six helpers without anything happening in game (just don't summon anything while a summon is still in progress - you'll lose your mana and not gain a companion)
This game is awesome, reminiscent of the old arcade game. Very addictive. It would be nice if it remembered your sound preference and if it had a sound volume slider instead of just an on/off switch. Great work!