I actually think a saurus oldblood on cold one is really good if you use it like this:
Oldblood, Cold One, Piranha Blade, Armour of Destiny, Shield.. for only 246 points (correct me if i calculated wrong)
You have an oldblood with WS 5, Str 5, 5 attacks, Multiple Wounds (D3), 1+ as and 4+ wardsave.. You are able to increase strength, toughness and attacks with lore of beasts! Makes a real monster and character hunter..
To answer the question, why no carnosaur (if people want to ask), because a carnosaur can be sniped by warmachines like rocklobbers, cold ones don't.. And I think 5 attacks (which can be increased to 8 with lore of beasts) would be enough to slay a monster in one turn! Usually hitting on a 3+ with PF!
I think we got a real powerful new armybook, you only have to combine the right units!
Tactics like using saurus warriors with jungle swarms, Poisoned on a 6 and a free extra attack..
Only bad thing is, PF only works for the first rank.. supporting attacks may only make one single attack, regardless of any special rules, no exceptions.. Nevertheless still a few extra attacks, more change to kill!
Other idea is using a signature slann, cast the mystifying miasma to reduce WS, cast iceshard blizz to give a -1 to hit penalty and boost your unit, for example, of saurus warriors with +1 strength and toughness...
Result: enemy hits at least on 4+, normal units usually hits on a 6+ and wounds you much harder, if you reduce enough you hit the enemy on a 3+ instead of 4+ and wounds on a 2+ or 3+ when targetting normal units!
Almost the same combination can be made with a loremaster HM slann and a lv 1 heavens wizard with signature, you only are missing the +1 strength and toughness, but can be gathered by changing a spell from HM to Lore of beasts!
These are only the basics of the lizardmen, didn't talked about rippers, stegadons and more!