[SOLVED] Spawn wither skeletons in region with normal skull drop

Im new to this plugin and i'd really like to learn how i can make a region where wither skeletons will spawn.
Right now im not looking for anything fancy. I have made a custom nether fortress in a custom world (Multiverse-Core) and I want wither skeletons to spawn and drop skulls like normal. I understand how to add custom armor to the skeletons, so i'll mess around with that, but I would be very thankful if someone helped me out with how i can create a spawning region for the skeletons. Its...

[SOLVED] Spawn wither skeletons in region with normal skull drop