From the announcement:
We are releasing two new armies again, as well as bringing some smaller updates. There were some people requesting these ones so I’m happy to deliver more ways to play for them. :)
Dark Elf Raiders are evil elves that live off of piracy and slave trade, looking for revenge against their High Elf brethren. Their playstyle is very fast and they sport some of the deadliest weapons in the game.
Mummified Undead are the deserty counterpart to the Vampiric Undead, bringing skeletons and animated constructs to the table. They can be played both as a horde force with large blocks of warriors, or as a small elite force with monsters and guardian statues.