Pixel Dungeon

Unlockable Huntress Character Class:
When you have defeated the the third boss the Huntress character class will become unlocked.

Unlock Challenges Mode:
When you have completed the game Challenge mode will become accessible when you select a hero.

Rat King, Depth 5
In Goo's main chamber, there is a secret door to the Rat King's room. It contains lots of chests most with low gold, but some armor and weapons.