The chocobo riding glitch in the SNES and PS versions of Final Fantasy VI happens when a guest character is the party leader and the player tries to ride a chocobo. The only instance in which this glitch occurs is during Banon-Edgar-Terra's scenario, after they reach the end of the Lethe River and arrive on the overworld map. There is a hidden Chocobo Stable in the forest on the edge of the desert just southwest of Figaro Castle. If the player rides a chocobo with Banon as the party leader, his sprite will appear to be glitchy, with the lower portion of his walking sprite animation pasted on the chocobo's back and his head being cut off. This glitch was fixed in the GBA version, in which Banon's riding sprite is replaced with Terra's. This glitch was also fixed in the Pixel Remaster, where Banon was given new sprites.
The reason for this glitch is because guest characters have not been assigned any chocobo riding sprites, and no riding sprites are at their disposal since the developers have not given them any, possibly due to them being temporarily playable characters.
This glitch can also occur with Leo, a permanent Terra in her esper form, Locke in Merchant clothes, the two Ghosts, and Kefka. These characters must be hacked into the party with a cheating device in order to see them glitch, as, unlike Banon, they cannot encounter a similar situation when playing the game normally. Merchant Locke is an exception; he can be seen without hacking by exploiting the bypass event glitch.
There is a bugfix patch that the player can use to fix this glitch in the SNES version. Unlike the GBA version, this fix adds a new riding sprite for Banon.