Bit of an oldie from September.
 
While dragon/pony hybrids can have wild physical variations, including presence of a Cutie Mark, scales, horns (both magical and non-magical), etc., the ten Invictus siblings (and by extension, those of their descendants that posess antlers) all shed them every 5-30 years at the onset of winter or when sufficiently damaged. It takes a few months for them to grow back fully, never quite having the same shape every time, and for those that don’t have a unicorn horn it means no magic until they reach a specific size.
 
(Wheatley also had the tendency to hide his blinded eye with an eyepatch, the doof.)