To anyone needing to beat the boss,
make sure you have maxed out health, gun ammo and pwr. You also need enough jump to reach the shortcut when u go left from spawn.
Basicly, during the boss fight, dodge the random shots it shoots out. Once it starts shooting in a spiral, stay beneath the boss. Soon, the boss will be shooting straight down, but as long as you stay between the two streams of fire, you're safe. Once the boss stops firing and flies up, move out of the way and avoid it squishing you. Then when its stunned on the ground, let loose your fire, remember that the boss is stunned only for a few secs, so you'll have to redo the process.
Hope this helps, my 1st helping post.