Ok, so basically, I was thinking, you know how I made my resource pack loot code for the Wither to drop the Soul Stone? I thought maybe it would be cool for him to spawn in as a rare natural Nether mob. The only problem with that is MCreator is a sassy little b word that doesn't agree to cooperate with things, so I couldn't just do a simple 3 by 3 structure NBT save of the Wither, as it could just spawn it in blocks or lava and kill the Wither via suffocation before the player even reaches it. So what I did was, using WorldEdit, I created a 32 x 32 (and a height of about 9) area of cool terrain. Now, I was planning on making multiple ones for different shapes and sizes, but as I said, the evil MCreator overlords made it practically impossible. Also, the best way for it to spawn is on/around lava lakes, so like I said, the terrain might be weird. In future versions, I might make it so some small bone block structures will also spawn in Netherrack, but I might not make it for a while unless you guys say you want it in comments.

IMPORTANT PART STUFF KINDA

First thing to acknowledge, MCreator isn't perfect, and neither is any mod-making tool really, so it might spawn in messed up and can also be rare. 

Here's it even in a Nether Fortress

And this one is one below, so warning: it might even go under some.e

Also remember: somewhat rare, but with the bad stuff out of the way, let's move on to the good stuff (also ignore the sign; it was a working prototype; it isn't included)

First thing is it comes with its own bone structure, so if you use X-ray, which honestly, since times are hard, I'll leave a related link in Relations to find the bone block to help find it.

Next thing is natural wither skeletons, but just to let you know, read spoiler if you want to find out how the skeles spawn naturally

Here's a picture of a bonus thing; if you have the mod Future MC, which I'll also leave in relations, you will have wither roses spawn. Weird fact: wither skeletons are not immune to the wither effect; I honestly thought they were. And don't worry: if you don't have Future MC, it won't crash your game; it will just simply not spawn in the Wither Roseses.

All in all, it will probably look something like this if you find one, and good luck. If you want the cool orange look and glow and name, look at my "Soul Empowered Wither" resource pack. id is =1724567

Also, lava can spawn in it as a cool terrain blend, but it can be dangerous.

Bonus FUN FACT

If you want to fight Wither skeletons and not the Wither because you're undergeared, or simply think it'll look good as a Nether Wart farm, simply turn it to peaceful and back, and the Wither is gone; the important thing is the Wither skeletons.