The Truth Tortoise appears in Morty's Mind Blowers as the opening scene where Rick and Morty are running from the Morpheus (Sandman from Neil Gaiman) with the Truth Tortoise. Rick mentions to never looking its eyes because you'll know everything.
The tortoise then says "Daed si luap, eltaeb a mi" which is backwards for "im a beatle, paul is deaD" which is a reference to a conspiracy theory that claimed that Paul McCartney from The Beatles died during 1966-67 and was replaced by a look-alike. Justin Roiland actually did the voice for this part.
Appearances
Season 3