There are 5 bosses in the game (SCREEN CAPS NEEDED!).
The bosses appear after every 2nd level, or when you use one of the special summoning runes.
First bosses Edit
Eyelo: A single large eye that moves in a diagonal line until collision with a wall then bounces, and also occasionally shoots lasers in along its x and y axis from the center of its pupil.
Cyclo twins: Two smaller eyes that move similarly to Eyelo, although they do not fire lasers. They have separate health bars
The second level's boss is: The Guardian, a large, golem-like creature, who shoots lasers from his eyes and slams his fists down whenever you get near him.
The third level's boss: Cobra, a large snake, who you fight in a room full of fireball-spewing lava, and rocky platforms. Cobra will surface above certain platforms around the room, and although he doesn't attack you at all, the lava and fireballs are definitely something to watch out for. The trick to killing him is to wait until he surfaces, jump onto his pedestal and then attack him. Use of ranged weapons is highly advised.
The final boss is: Dark Mage Gideon, the wizard that you can see when clicking on the "story" option in the main menu. His abilities are splitting into 3 separate entities, then firing out projectiles at the player. After each time you successfully attack him, he will spawn either a ghost or a fire skull. Defeating him will trigger the end cut scene.