If Tyion is in the center of the unit it is hard not to get him into base to base; however, frequently characters are simply put on the side. This allows for the opportunity to engage the unit without fighting Tyrion. This will only happen against sloppy players, a top tier player wouldn't make that mistake, but then, you have other problems.
The absolute best way to kill Tyrion is killing blow, the bypasses the armor, and regeneration, however, only one thing in the lizardman list has killing blow making that a little difficulty.
The best solution would be to ignore him. He's alot of points, so is his unit, add them together you are looking at 750 points easily. At this point you can feed him a skink unit every turn for the entire game and still not be behind.
Set up something like this.
He will have to charge your skinks, they are in his way. However, when you flee he must persue the closest visable skirmisher, the guy in red.
This will pull his unit WAY out of possition.
Plan turn one, he moves forward.
Turn two he charges your screen.
Turn three he has to turn around.
Turn four pull him off with another screen.
Turn five he is getting back in possiton.
Turn six game is more or less already over, if you need, throw him another unit.
So for 2, maybe 3 screens, you are fine. He just had a 750 point unit kill 200 points, sounds like a great trade to me.
Now, the hard part of the game is setting this up. It takes practice and skill, but onces you get used to doing stuff like this you can mitigate just about any deathstar unit.