FinalBoss refers to the gauntlet of bosses fought in Final Climb. He is the leader of the ghosts that forced the birds away from their ancestral home atop The Curtain. He has a lackey that he sends out to deal with minor foes. His boss battle is separated into five forms, or four in Simple.
Throughout the battle, as each form of the FinalBoss is defeated, he leaves behind a purple glow, and it is unknown, due to the screen whiting out, whether this escapes after the final form.
FinalBoss' first form takes the form of a purple hooded figure, who looks similar to TheBoss from Jumper, except for the difference in colouration. His battle involves periodically shooting out homing balls, followed by one charge shot. This charge shot will be launched towards the bird, and rebounds once it hits the platform. To damage this form, the player must position the bird so that the charged shot rebounds and hits the boss. On Masterful and Insanity, it takes three hits to defeat this form. Homing balls can be shot.
During FinalBoss' second form, the floor disappears, and the he reappears in the form of two purple rings. Red energy then appears around the room, which must be bounced around throughout the whole battle. The rings move erratically around and create a laser between them periodically. In addition to this, on harder difficulties, they also shoot out purple laser shots in the direction of the bird.
To defeat this form, the player must wait for the rings to turn white and then jump on them. Each ring must be hit twice. When one ring is killed, the other is robbed of the ability to create a laser, and it takes a significantly less amount of time to turn white.
In the third form of FinalBoss, he falls from the sky and lands on the newly formed ground. He paces back and forth across the stage while shooting purple lasers and the same white homing balls used during the first form. During this battle, the player should try to stay on the side on which the boss is moving away from.
After a while, the boss will fire a sweeping laser. This laser will rotate 180 degrees on Masterful. After firing the laser, he will turn white and becomes vulnerable.
On the fourth form, the legs disappear and FinalBoss begins flying around while shooting purple lasers. The flyer flies back and forth until it goes near the ground, where it turns white and can be hit. After this, it descends. This must be hit three times on Masterful, and does not appear on Simple.
The last form is a survival endurance test, in which FinalBoss continually shoots out purple lasers, homing balls and two new weapons. The first is a firework-esque attack that shoots out lasers in eight directions multiple times as it falls. The second is a purple column that appears and spreads out into a laser column similar to StoneEye's except vertical.
The only change between Masterful and Insanity other than dying in one hit is that the player must endure two minutes of the attack rather than a minute and forty-five seconds on Masterful.
In Simple during the dialogue just before the final fight the player gets a heart which refills health.