Contains 4 extra cards. You need at least a copy of Rattus, the basic game, and the expansion Rattus Africanus to be able to play with these 4 cards.
Can also be combined with the Rattus expansion Pied Piper (in combination with Rattus, the basic game, and Rattus Africanus).
Amongst the 4 cards are Aladdin and Sinbad.
For more information: http://boardgamegeek.com/boardgameexpansion/108186/rattus-bonus-2