One of the best players at my gaming store plays Tomb Kings. I had a Lore of Death Slann take out his heirophant in round two last game and he still beat me by a wide margin. He positioning was superb so I was likely to lose anyway, but I felt like my skirmishers were just free points for him. I know if you are building a list to play TK, Chamo skinks are a waste of points because TK missile troops ignore all penalties to hit. Lets say I have an all-comers list, and my all comers list has several chameleon skinks in it. What should I do with my chamo skinks against TK? It seemed that there was nothing my skinks could do significant damage to and no enemy unit which couldn't kill my skinks with minimal effort. What CAN I do with chamo skinks when fighting Tomb Kings, so they aren't just free points for my opponent?
Redirecters, monster hunters, and pincushions. If he's wasting shots on them it means he's not softening up everything else.
When my oponent guards the casket (or cannon, or whatever), I just put my chameleons 12 inches away from his line, closest to the target. Then march to within 1 inch of the unit that is guarding the warmachine. If I have to single tap, I will do that. The time my oponent takest to remove my chameleons is time spent not focued on my other troops. Something to watch out for is the Herotitan. That thing generates d3 to each spell cast within 12 inches. It is brutal when added with the casket (which gives d3 power dice as well).
I think that Sphinxes of all sorts are good targets for Chameleons if the Casket is too tightly guarded. Tomb Kings hate it when you poison their stone statues...