Sweet Celestia, I cannot stop drawing Yosh-E-O! I love his adorable character so much, I have like 5 other pictures of him too.

In this picture, Spike was on vacation (to a beach far away where he's getting nose bleeds from looking at all the attractive female ponies) so Twilight needed a temporary new messenger. Since Dawnbreak Horizon was also on vacation (at that same beach, also getting nose bleeds), Yosh volunteered. Since Yosh couldn't teleport letters the same way Spike could, he had to deliver them by means of a magic onesie developed by Celestia. This Onesie allowed him to fly, though only to one or 2 locations on a fixed path.

On this day, Yosh accidentally dropped the message for Twilight. As he bent over to pick it up, Twilight got a good look at his padded rear, which looked like it was about to break the onesie. Twilight asked if Yosh needed a diaper change, to which Yosh said this was how thick his diaper was all the time. One of the buttons then broke off and hit Twilight in the head, knocking her out. Maybe Celestia should have just made some magic diapers for Yosh.