There are two abandoned floors in dungeoneering. These floors are found at floor 12-17 and 30-35.
Starting out in the abandoned floors.
Monster
These floors contain monsters such as:
* Forgotten warrior * Forgotten ranger * Forgotten mage * Mastices * Giant rat * Mysterious shade * Earth warrior * Dungeon spider(m)(p) * Skeleton * Zombie * Crawling hand(m)(s 5) * Night spider(m)(p) * Green dragon * Pyrefiend(m)(s 30) * Hill giant * Cave crawler(m)(p)(s 10) * Bat * Giant bat * Hobgoblin * Giant skeleton * Animated pickaxe * Jelly(m)(s 52)
Bosses
Abandoned floor 1
*Bulwark beast *Hobgoblin geomancer *Skeletal Horde & divine skinweaver *Unholy cursebearer
Abandoned floor 2
*Bal'lak the Pummeller *Shadow-forger Ihlakhizan *Unholy cursebearer
It is still unconfirmed whether it is possible to fight all abandoned floor bosses in abandoned floor 2.