undertale-science:

We all know that Reaper Bird, also known as “,” is made up of Astigmatism (obviously) and also Final Froggit and Whimsalot based off the check message and quotes. Read about that here. 
What many people don’t understand is that the body of Reaper bird is stretched out in battle, the actual sprites for it’s body are much shorter.

The animation actually shows how the parts come apart and melt and deform, then come back together. This allowed me to see how the torso is really Final Froggits dismembered legs rotated and flipped then joined back together attached to the legs of Whimsalot. The think keeping it together looks like electricity zapping it back together in an arc like a bolt of lightning. I decided to color it yellow because the closest thing to it would be Whimasalots weapon, if not, then its just electricity.

oh, and another thing, Reaperbird isn’t turning its head, sprites show that the beak (made of Astigmatisms legs) actually goes around the “head” to the other side, with the eyelashs and spikes shrinking and growing.   

Sprites in original size