Wither plague

We all know the wither, but it can easly get lost, and 3 wither skulls are hard to get. Let's make the wither follow the player permanently and make him control mobs, making near mobs get sick and attack players, just in the story mod! Let's make it have a small chanche to produce fire. If the wither stays without dying 40 minutes, it gets bigger and more dangerous, to his last phase.