"Rage Against the Vaccine" (FUTURAMA S11E07) had a parade of fairly obscure recurring characters. I love that nothing and nobody on this show is ever forgotten.
Father Changstein El-Gamal!
Dr. Banjo!
Jrrr!
Horrible Gelatinous Blob! (The lady in purple looks familiar, too. At first I thought she was Colleen from "The Beast with a Billion Backs," but I'm not 100% sure.)
The Spice Weasel!
Umbriel and the Colonel, the merfolk of Atlanta!
And sweet llamas of the Bahamas, it's Barbados Slim!
I don't know if Scoop Chang and Judge Whitey really count as obscure anymore, but their appearances are infrequent enough to make me happy whenever they crop up.
And I really hope Bonebot won't be a one-and-done character. If The Borax Kid cane come back three times, surely there's room for more groanworthy skeletal puns.