They are egg shaped ships with a red paintjob on their tip. They have engines attached to them, out of which they shoot eggs.
The editions do not alter them at all.
They appear three times in Revenge of the Yolk, in Waves 25, 53, and 85. In Wave 25 Eggship fly-by, they make arcs around the center of the screen. In Wave 53 Eggships approaching from behind!, they arrive from the bottom of the screen and fly up in a curvy path. In Wave 85 Eggship fly-by, they do the same thing as in Wave 25, but this time they do it around the center of the sides of the screen. In the first wave they appear in, they have 1400 health. In the second, they have 2000 health. In the third one, they have 2600 health. They will always give 7000 points and 1 coin after being destroyed. They may also drop a Powerup.