In Trivial difficulty The Yolk Star uses 4 laser cannons and 5 cannons for easy difficulty. When %50 of its health depletes, it summons only a chicken (Chick or non-metal suited) and once its health completely deplated, the shell will be exploded.
In Intermediate & Hard difficulties The Yolk Star uses 6 laser cannons. When %33 of its health depletes, it summons a chicken. After %66, it summons 2 chickens and once its health completely deplated, the shell will be exploded. Pilot & Metal-suited & Toxic and UFO chickens will appear.
In Very hard & Elite difficulties The Yolk Star uses 7 laser cannons. It has the same progression about summoning chickens. Chickenaut & Slob Chickens will appear and harder chickens I don’t know their names.
P.S. Both Yolk Star and Egg Cannon should drop a satellite (like Henterprise), when the shell of Yolk Star cracked or the purplish explotion appeared in Egg Cannon. (Thanks to @B256 for reminding)
I hope you interested with this and share your comments. Thanks!