Zedwork

I'm just sat chilling, heading a zombie spawner. I see a skeletal horse in a tree so i head towards it trying to tame it then next thing lightning hits the horse and 3 skeletons riding skeletal horses appear and start shredding me. Then when I kill them I go to take a horse to my pen and more lightning hits just outside my sheep pen and more skeletons riding horses appear. Is this actually a thing because if so that's amazing but I pooped myself twice in 2 minutes, not fun!

This is a new occurrence that happens in Minecraft. When you are near a skeletal horse, there is the chance that lightning will strike down upon the horse and create 4. This is known as the 4 horsemen, dating back to biblical history, and they are skeletons riding skeletal horses that have iron helmets on them. They added this in the 1.9 release and is one of the coolest mobs in the game. This is what the hell just happened. xD

I don't think its any random skeleton horse. There is a small percentage that allows a skeleton horse to spawn and when the player gets within X blocks it gets struck with lightning. But I don't think it can happen to a skeleton horse you already encountered.

Yes it's thing.

Also, with the location of your base it will be loaded fairly often. These trap horses have a chance to spawn with lightning strikes and these are the ones that spawn the 4 horsemen. You were just unlucky to get a few next to each other.

Yes, this happened to me twice in the first week of 1.9 and it scared me which was a nice unexpected surprise.