Changes to the summoning of the Wither

I strongly believe that the Wither must be a Nether World exclusive boss; only capable of been summoned in the Nether and no other worlds. However, the boss cannot be summoned anywhere in the Nether but on a special platform surrounded by a terrain built to the Wither's advantage. This will impose a great challenge facing the boss because not only will you be worried about the Wither but also be worried about falling down a cliff or into LAVA.