User blog comment:ShadowEyepatch/Shadow Deities/@comment-7341673-20160504130647

Just my thoughts here, but:

1. It seems kinda strange to call the clan "Shadow Deities" and then call their keyword "Shadow".

2. Maybe something like skill/power mirroring. Some kind of "1/Turn: Choose  another unit. Until end or turn, this unit gets that unit's skill" for some kind of "your shadow is the same as you" thing.

3. Could be cards hiding under other cards. Example: A rearguard goes to drop, you pay some cost, and it gets placed under one of your RGs face-down as a "Shadow". When the one it's under is gone, the other "Shadow Callls" itself and gets some benefit if it was Shadow Called or some skill depending on what it was the "Shadow" of.