In one of the timelines in the Multiverse, the monsters and bizarre creatures we think of as myths and urban legends grew stronger and stronger while hiding from the human race, which hated and feared them. Given enough time to flourish and multiply, they finally broke out of their hiding in darkness and obscurity, hellbent on revenge! They slaughtered their way through the human population of the world, destroying all they touched. The human race rallied, but ultimately, the monsters from their greatest nightmares were too strong and too numerous.
Decades turned into centuries, and centuries became millenia - the world, now overrun entirely by monsters of all sorts, is a terrible wasteland. The few points of light in the darkness have long been extinguished. This could be the most terrible era for heroes, lost in time, to end up.
Hope that you never do.
The Final Wasteland is the true end to all time. Do not think that you can overcome its dangers: pray that you might survive it.