Grifthin said:
Well 10 Chameleons are the same points as 4 terradons.
And If they are in cover it's -3 to hit the little buggers.
How effective would they be vs Dwarf crew though is the question.
Not very effective, but then neither would the Terradons be. The smallest unit that can tackle a dwarf warmachine with a near-certain victory rate is a skink/krox small cohort. All you have to manage to do is kill one dwarf, and you will auto-break them because of the Krox's US 3 fear (unless of course they have an engineer joined to the machine, in which case you need to kill 2). The minimum size of this cohort is 10sk/1krox for 105 points. And of course, you still have to cross the table to get the threat in their face. However, you might find dwarf warmachines the only thing worth going after with your fairly light cohorts. Against dwarves, terradons are best used to nail those lines of quarrellers and thunderers.
So either chameleon skinks or terradons can charge a warmachine and keep it tied up for a while. However it is important to remember that terries serve in a ton of other important and more "mobile" roles in the army, and the thought of having a unit of them tied up for one or two turns in a warmachine combat makes me cringe. Think about it, a unit that can always move 20 inches not moving even for one turn is sub-optimal. If you have chameleons (preferably less than 10 though!) they can scout and get to a machine in probably two turns.
The rare case it might actually be a good idea to charge WM with the terradons (given the option of chams or terries) is against Dwarf Anvil armies. Your terradons being in combat is the only way to protect them from Wrath and Ruin, and believe me when I say terradons make a very juicy target since they aren't allowed to fly for a turn after they are hit. A warmachine combat is the "safest" place for them in this situation.
Handy bolt-thrower or stone thrower tactic. Chameleons advance to point-blank range and spread out, making a line in front of the machine. Once you are close enough, you will block out all useful line of sight for the warmachine, whilst keeping the chameleons very safe. Bolt throwers will be at a -2 penalty to hit the little guys, and will kill a max of 1. I personally like those odds compared to hand to hand combat, plus the skinks will be dishing out 2 shots each, hitting on 4+ poison on 6 (once you've set up at close range). Stone throwers also have a minimum guess range of 12 inches, so they won't really be able to shoot at all in retaliation. As with all things, good judgement is required as to when to use this and when to just go for the charge.
Stubborn dwarf crews (of bolt throwers or grudge throwers) would probably be best tackled this way by the chameleons. Stubborn means the skinks will probably have to kill them all anyway, they might as well kill them with a favorable shooting advantage.