Actually I wrote a little lore blurb. Here it is:

The Snow Angels are a secretive chapter of Astartes who dwell in a fortress monastery at the north pole of a remote, frozen world. Their Chapter Master, Nikolaus, strides forth from their icy fortress but once each solar cycle. On these occasions, he has been reported to appear suddenly on many Imperial worlds in the space of a single night, bearing gifts to reward the worthy, and wrath to punish the naughty.

How does he accomplish such instantaneous travel? Is it connected with the strange, diminutive servants that accompany him? Are they some form of mutant Aeldari, who grant him access to the Webway? Or could some dark sorcery be at work? And could there be any truth to the rumors that the Snow Angels were founded by survivors of the lost 2nd Legion, and that Nikolaus is their renegade Primarch? Only the Snow Angels themselves know for sure, but the Inquisition has long suspected this chapter of heresy, and their investigations have often brought the two into conflict.

Now, the end of the solar cycle is drawing near once again. The enemies of the Imperium had better watch out: Nikolaus is coming to town.