I like the idea of a Tomb Skeleton commander well enough. They're some of the less appreciated squads, I think, and they could function well as dungeon crawl baddies. I do have some quibbles with the design that I think could be improved, though.
Frankly, I think that Skeletal Form is a bad power. There are plenty of Clerics and Wizards with 1 range (some of the most notable 'Scape Wizards use 1 range and a Special Attack), and the power still works against melee attacks from ranged figures. It has always felt messy and too "metagame-y" to me. That said, it does make sense to reuse the Tomb Skeletons' defining power here if you want to tie the figure more strongly to them, and it
is an existing power already. I think that you can still convey the theme in a stronger way without repeating that particular mistake, but that might just be a matter of personal taste.
I don't think that Double Attack is necessary here. I know the mini has two weapons, but Tatomb is already going to get plenty of attacks in by sheer virtue of unifying two Common Squads. I think that it makes sense to let the skeletal hordes shine in this army and have Tatomb act more as a commander.
I agree with Scytale on Captain of the Guard; it'd be much cleaner and probably achieve much of the same mechanics if the requirement was only that the activated squad figures begin their turn near Tatomb rather than away from him. The skeletons will still want to clump up to a certain extent so that they can leverage the bonus activations, even if they have the option to split off as needed.
Thematically, "Captain of the Guard" as a name sounds a bit too vague for what is very specifically a
Tomb Skeleton power, even if they are guards. I would suggest "Captain of the Tomb" or some equivalent (or perhaps even a class of
Warden with a matching power name, to better display Tatomb's status above the other skeletons). The Guard class is neat for its synergy, but I think that the added theme is worth considering there. Alternatively, you could take the opposite approach and throw some Guard synergy into Captain of the Guard a la Kato Katsuro, though I can't say that I'm personally super fond of the idea since it encroaches on what made that power special.
Also, why does Tatomb follow Vydar? The stats and powers seem to suggest that this is a beefed up Tomb Skeleton. Valkrill feels like the natural choice here.