Units of 5 vanilla knights can be very useful against skin spam. The 1+ save combined with their pathetic combat potential is very nice. 5 knights can easily route skink skirms. Even ranked skinks will struggle to wound, and even horses wound on a 3+.
These screening knights are great, but their solo scar vets and old bloods destroy anything with armor. s7 with at least 4 attacks. 1+ saves with either dawnstone or a 4++, cause fear, cold blooded means they can tarpit many units. They can also kill steamtanks. Be very wary of these guys. Demi's and IC knights on the charge are you best bet. If you can't break them on the charge.... well good luck getting through the T5 1+ save.
These knights should also be used to screen your warmachines form poison shots. Once they get close, charge them outta the way. Even light magic missiles kill skinks, T2 is bad. Don't let these guys kill your warmachines, this is their only real role vs The Empire.
Chameleons are WORSE than skinks. They're at a -2 to hit with missile fire, so charge them, or magic missile them. They are scouts. I highly suggest denying them deployment on your flank, and placing your vanilla knights between warmachines and likely chameleon deployments.
Salamanders will deplete any infantry block/horde quite horribly. These things need to be shot, or engaged by a capatus ASAP. They can't form ranks, so do some wounds on the charge, and send them packing. If possible target the skink handlers, they are easier to hit and wound.
Saurus are ok, but still WS3, I1. You have several options. Out buff them, or out debuff them. Lore of light will see halbs making mincemeat of regular saurus. Purple sun or Pit of shades ends them, heroes included. Lore of shadow is classy b/c you can take both of their good stats, T4/S4 down. Miasma can do the same with their already poor weapon skill.
Stegadons are big, but only do damage through impact hits and stomps. Deny these with knights. They have few attacks, but are stubborn. Chickens can topple them. DO NOT let them charge an infantry block, esp one which is already in combat. Oh yea, shoot cannons at them.
Terradons can kill small chaff units, even skirmishers very easily, by dropping rocks. D3 auto hits per rider if they fly over. They can only do it once, but it hurts.
If you're tailoring a list, forbidden rodding a purple sun through his TG unit may be an autowin for you. I'm becoming less and less of a halb horde fan as of late. (unless I'm running lore of light) Your 1+ saves can save you a lot of grief. Have patience. A TG unit with a slaan looks VERY juicy, but its equally as hard to remove via combat. Stubborn, cold blooded, with the general and bsb slaan in the 2A S5 unit is rough. Esp if he plays keep away with this unit. Focus on where you can get easy points, LM give them up all over.
