As with any scary beast: "Kill it with fire! is a solid advice.
Even in the Warhammer world, where a lot of beasts have regeneration. Use a fiery weapon to negate it and then fire your poisoned shots at it.
Any weapon that deals multiple wounds is ofcourse ace, weaken it with skink-fire and then move in for the kill.
Chameleon skinks can start shooting from as soon as turn 1!
The downside to blade of realities is that it just costs soooo much...and the heroes that you would want to insta-kill (goblin bosses don't count..) have a high leadership, so they will not go 'poof' anytime soon. Add in a BSB and I think you would be better of with an entirely different load-out for your old-blood.
But, try it, see if you like it and then change if needed!
The Hunted