Squidly Tentacles only appeared in Dunces and Dragons, in which he met time travelers SpongeBob and Patrick and set out to rescue Princess Pearl. They succeeded, and, at the end, Squidly accidentally went to the future, to SpongeBob and Patrick's time.
"Does thou talketh to me?"
"Scoff not, young squire. Thou has mistaken me for another. I am Squidly, the king's royal fool. Or at least I was until I royally messed up."
"Everyone be-ith a critic."
Squidly may be the reason Squidward is such a terrible clarinet player since Squidly cursed his future descendant.