Shleipnarr is a gorgeous fiery horse that looks exactly like the warlock Felsteed mount (my mount of choice for the warlock ground mounts). This rare is also very likely a reference to Sleipnir, the eight legged steed of Odin, one of the Norse gods. I hadn't realized this until I had read Navi's post: My favourite rare spawn(s). Here is the Wikipedia entry for Sleipnir for anyone curious: Sleipnir.
Both Slave Master Blackheart and Smoldar spawn underground in the Slag Pit, so if you don't run into them where their dots are on the map below - don't worry, they may still be up. If you don't use SilverDragon, just do a /target Slave Master and /target Smoldar to see if they are. Slave Master Blackheart spawns in the Slag Pit, right in front of the Quarry Gate. Smoldar spawns down in the lava pool right before you get to the Flamewraiths.
|Click Map to Enlarge|
|Faulty War Golem, Shleipnarr, Highlord Mastrogonde & Rekk'tilac|
|Scald, Slave Master Blackheart & Smoldar|