If possible I would test for MG, MS, Avian Tuberculosis, Mareks...... but I'm afraid Mareks is one of those that need a necropsy...
All of those can have paralysis accompanying it.
MG can be hidden in the bird, becoming a host, and that bird can seem fine... but it can spread the illness to others with out ever getting sick itself. that is called a carrier state. Others may show no signs of being sick until stressed somehow.... who new birds could be so complicated.
never really found out what it was, they replaced all the chicks, for me and many customers... but i had problems for a long time. I put a lot of birds down, and restarted from almost scratch.
Bird illnesses are never easy.
Your big guy looks very much like a Silkie cross I had named Peanut.

MG can be hidden in the bird, becoming a host, and that bird can seem fine... but it can spread the illness to others with out ever getting sick itself. that is called a carrier state. Others may show no signs of being sick until stressed somehow.... who new birds could be so complicated.
never really found out what it was, they replaced all the chicks, for me and many customers... but i had problems for a long time. I put a lot of birds down, and restarted from almost scratch.
Bird illnesses are never easy.
