In my Out of the Abyss game, the party adopted Stool, but brought him home. They invaded the Hook Horror nest and took one of the eggs. When it hatched, they named it T.J. Hook-Horror. When it grew to full size, it was one of the scarier members of the party...don't know what it was, but it would consistently roll really high and critical hits. They started casting Magic Weapon on it and adding it to their front line. At one point, T.J. got dominated briefly and attacked the party, rolling 2 crits in a roll and nearly dropping the Paladin, forcing the rest of the party to run.
We had a blast with him! The party started speculating that he was possibly one of the Demon Lords in disguise...