All those would work. Hmmmm...
"These appear to be garden-variety kobolds, but they move with an unusual unity of purpose."
Crypt kobolds are a recent magical alteration, bred by an unknown and perhaps unbalanced wizard who experimented on the hapless humanoids. While some have escaped his service, they are most comfortable frequenting underground crypts and tombs, such as the one they were created to guard. And those still loyal to their creator may receive aid against invaders in the form of summoned fiends.
As usual, that can probably be touched up a bit.