A thing that should apply to both the twins and the Eye of Cthulhu:
Please reduce the color banding, it kinda doesn't fit with Terraria considering the sprite updates done with others, and especially when the moon lord was introduced, and had a gorgeous sprite all around. One way to reduce said banding would be to add more colors between the existing ones on the eye whites, as well as a bit of dithering to go along with it.