When horses are under the invisibly effect horse armor don't even show up when zombies husks and strays and players wearing armor they show the armor when under the invisibly effect and this also happen with pig wearing saddles and horses wearing saddles how to repeat 1. Spawn or find a horse 2. Tame the horse 3. Put horse armor and a saddle on 4. Throw a slash potion of invisibly at the horse 5. You don't see the horse armor or the saddle