Our GM teased us with the opportunity to give us a follow up game for our group (prince and snakes) and inspired me to reflect on Shackil's past))
Given the complacency and arrogance of the character, I believe that he was under the illusion of his inviolability for a long time. That he is a fully-fledged member of their society and can rise to the point of becoming a true yuan-ti. But it seems that some of the higher-ranking yuanti got fed up with his complacency and he was pointed to his place in society. And I must admit, in a rather harsh way. He was hinted that he could always become prey like all other races, which they looked down on and used as victims in their rituals and experiments. For Shackil, who until that time had always been only in the role of a predator and looked down on the others, being on the other side was .... a very unpleasant discovery.
At first, I thought that he was initially aware of his lower position in yuan-ti society, but then looking closely at his character and behavior at the games, I thought that the transition should have been abrupt, unexpected and shocking. Otherwise, the nature of the character as well as his goals would be different. And he probably wouldn't be so interested in resurrecting their empire.