This is our "Realm" Planet Blacklight's Mob Arena... It's as simple as it could possible get: Simply walk inside and press the button on your right to initiate the "first wave" of mobs. You'll notice that there are plenty of obstacles and even stuff hanging from the ceiling. That's because there is a bit of "parkour" within the arena and if you're able to reach the ladder there is another room and a door to the roof area where you'll notice a cannon... for no reason.

The redstone mechanisms are encased within the obsidian below and beside the building. You can always access the dispensers and edit what mobs appear. Other notable items are the lava trash can outside and the emergency escape hatch within the arena; it's also advised to have an ender chest or other method of storing equipment prior to entering the arena.

In our realm the "escape hatch" drops you into a safe but sewer area where you can hide, heal or just escape the mobs and get out of the arena. I added a normal way out but you can delete them for the added effect as we have; both options are open or easily erased.

The top room could be used to drop a Zombie spawner (or any other mob) or allow for a "bonus room" while the cannon is just added for decoration. I didn't feel like erasing it... I had already cut all the stuff out around it, dropped it into a flat land (sorry for any snow) and picked away all the unwanted extras.

NOTICE : Lava not included.