Is it legal to combine a kroxigor into a group of skink skirmishers? I do not want to use them as cohorts, just provide a little shielding for my Kroxigors to get into battle.
You can't as Krox are an upgrade for Skinks units and not Skinks Skirmishers. That doesn't mean you can't use the skirmishers to screen a unit of Krox though.
You can still do this, they just would be separate units. Skink skirmishers are about one of the best screens in the game for the points.