Although this is not a Hybrid, it is in the same Piercing the Shroud mission. A Pygalisk is a small version of the Ultralisk, with only 50 health, and is a little smaller than a Zerg roach. It probably takes only 1 supply, and if it is in the game, it will probably be positioned between zergling and roach. One zerg unit idea that I think was unfortunately not implemented is the concept of a growing zerg. You start off with a Pygalisk, then it grows into an Ultralisk, and then to an Omegalisk. Each time it grows, it takes up more supply, but gains more health and damage abilities. It would be like a long term unit that you must incubate to really get good return. A Pygalisk pops from its own special type of Pygalisk Cocoon egg.
Pygalisk Cocoon egg: