You can get a harder version of the game by beating the Wall of Flesh. You have to drop a Guide Voodoo Doll into lava (works only in Underworld). Once you've beaten him, the game will get harder + more enemies. You can also unlock new ores by destroying Demon Altars using the Pwnhammer dropped by the Wall of Flesh.
There's also a new biome called The Hallow. There unicorns and pixies. But mostly unicorns. It's pretty much the opposite of Corruption.
Last edited by Luminusian; Dec 8, 2011 at 06:31 PM.