As Rare points out "Ideea...." get a pony plushie, remove part of the stuffing (not all, it should need some on head, body and hooves) get one of those horrid robot pet-dogs (g1 sony aibo's are dirt cheap now) and put it in the pony, like a glove, if well done, stuffing should not interfere with mechanism (better, put dog legs in a latex glove / sleeve so fuzz cannot get in them)
Theorically and depending of fabric, the aibo's nose-camera would see thru, a couple of IR LED's could provide additional light to counter light shaded by the fabric (dark coats would hinder more than white ones), anyways, the white balance of camera must be set to low kelvin value, so human recognition is attained.
The last, but not least for welder happy operators, involve modifying AI program stored in a memory stick to more pony like patterns, additionaly, two piano wire lines could be used to operate wings in pegasi (piano wire could be attatched to hind legs in a push-pull way)
Sadly, I lack motivation or sewing experience to make the aesthethic part of this (Plushies are pricey) and G1 aibos still ar 200$, so I give away my idea. Hoping someone could bring it/ somehow use.