Unleashed said:
In theory, they seem good - you get the strength and armour of Krox, and most of the time combat units will only be able to attack them. You get the shooting and bonus attacks of the skinks.
What's wrong with them in practice?
What is the unit good at? Well, you've got a few (9 or less, usually 6) very high Strength attacks, and plenty of cheap but pretty poor quality ranks. This isn't a unit that is going to do well at killing ranked infantry because it simply won't be able to deliver the volume of attacks needed to win.
So what are limited high strength attacks good at? Killing limited number, high Toughness/high Armour Save models: Cavalry, Monstrous Cavalry, Monstrous Infantry, Monsters, Chariots, etc. Great! Let's go find those to fight.
Except... the Kroxigor can be attacked in combat so long as you are in base contact with a Skink. The Kroxigor only have T4 4+, and with their Great Weapons Always Strike Last. All those things I listed above, for the most part, tend to have a high damage output (At least on the turn they charge) - So they can direct all their attacks against the Kroxigor, wipe them out or reduce them to the point that the Krox WS3 makes any surviving attacks pointless because so many miss, and then spend the next turn crushing Skinks until the unit breaks and flees.
About the only ideal thing that they are good at fighting is Cavalry who haven't charged and don't get lance/spear bonuses, or flank attacks on Cav/Monstrous Cav/Inf. Magic does also help shift the balance in their favor (that old Lizardmen chestnut...).
So whilst they look good on paper, finding a worthwhile match up in practice isn't as easy at is looks.