Sparklite

This is the final boss of the game and he shouldn't be much of a challenge if you're properly stocked up with upgrades and health widgets. If this is one of the last things you do in the game, you should have enough damage and health upgrades that you can walk through most attacks, making this pretty trivial.

This boss is the only one in the game with two different forms. The first is where he is human-sized, teleporting across the screen, using a handful of different attacks. Each of his attacks are easily telegraphed, as the areas where you can take damage will turn dark red before doing damage. Avoid his attacks and dash to him, getting in as many hits as you can before he teleports. At certain points he will teleport to the center of the screen, be aware that he sends out projectiles in a set pattern. If you know where to stand, you can attack him during the entire projectile attack.

Once you drain the boss's health, a cutscene will play and you will find yourself on a floating island with a ton of enemies. This section of the boss fight is just clearing out waves of enemies before stepping on the glowing symbol at the top of the screen. With enough damage upgrades, every enemy should fall in two or three hits, making this pretty easy. After the fifth floating island, you'll have beaten the boss and the game.