Chocobo makes your character grow.

[Lilyarel]

If you get on your Chocobo and walk to the left, you will grow. But if you stop walking you will go back to normal size. If you dismount while walking to the left, your character will be stuck at that height until you either leave the area or mount and dismount. A max height Roe will be about the same height as an Amal. You must walk to the left and you must be on a Chocobo. This bug doesnt seem to happen with other mounts. This also seems to be client-side, a person will only appear big if it happened near them. Otherwise they will appear normal height.

[viewtyjoe]

Additional information: this bug appears to occur on any mount that uses the same sitting animation as the Company Chocobo, as it occurs under the same circumstances with the Draught Chocobo and affects both players if there is a passenger, but does not happen with the Ceremony Chocobo, which uses a different animation for the rider in front (at least for female characters in our testing). The change is visible to any player who is in the zone when the walk left and dismount sequence occurs, but not to players who enter the zone afterwards. The size increase appears to be between 25-50%.