The so-called chicken rider is an NPC that spawn very rarely (IO think I read 1:3000 somewhere), although a "fake" version can be spawned using a complicated /summon command. The zombie is misplaced and flying above the chicken though in the /summon version.
Ha yes, Thank You jrg. I was going to fix it, but I lost where I saved the picture Then again I could've re-saved it but eh.