All munchkin sets can be played with each other but expansions work best with the main/deluxe sets they are related to.
Munchkin 8: Half Horse, Will Travelis a 112-card expansion forMunchkinthat adds two new races to the game: Centaur and Lizard Guy. A myriad other new cards are included, such as race/class enhancers (Elite, Legendary, and Elder) and monsters (Gecko On The Telly, Centaurpede, and the Knight Mare).
The name for this expansion was selected via a contest. Users were asked to submit entries, and the Steve Jackson Games staff chose "Half Horse, Will Travel" – submitted by Michael Shore – as the best entry.