Slann
Mystery
Rumination
Higher State of Consciousness
Cupped Hands of the Old Ones
BSB
I'd drop 'Higher State', he's going to get nuked by miscasts or by enemy magic/heroes with magic weapons. It's a nice trick, but I'd rather spent points on other gear. Banner of Eternal Flame is only 10pts and will make your Temple Guard hit harder. 'Cupped Hands' is a personal choice, I find it overpriced for a one-use item. Lore of Light is a pretty good one to take against vamps, and the WS10/I10 spell will make your Saurus and Temple Guard hit first against ogres.
I'd suggest taking an Old Blood to bodyguard your Slann with. Here is how I run mine;
Old Blood w/Giant Blade, Armour of Fortune, Potion of Speed
Strength 8 means vampire heroes get squished, he's got 2+ armour and 5+ ward, and when he pops the Potion he'll hopefully strike ahead of vampire infantry (already does against Ogres). He's basically my 'f$%& off' button for elite infantry hoping to roll through the Temple Guard into the Slann.
Saurus Scar - Veteran
Cold One
Burning Blade
The Maiming Shield
Light Armour
Unless you're taking Cold One Riders, I'd drop the mount, as ideally you want him in a Saurus unit, providing support. Burning Blade is a good choice. I'd drop Maiming shield, it's a lot of points and your shield slot used up for just +1A (and it's not even usable with Burning Blade, so whats the point?). I'll give you an example of how I would run my Scar-Vets (as I take two)
Scar-Veteran w/Burning Blade of Chotec, Dragonhelm, light armour, shield
This guy is a wyrm-slayer in my background for him, hence the loadout. Packs 2+ armour, has a 2+ ward against flaming attacks (which will be pretty common, with Banner of Eternal Flame being so cheap and the fire lore/flame templates being popular for burninating infantry). -4 to armour saves is always fun, as is being flaming and magical (plenty of flexibility with that combo).
Scar-Veteran w/Piranha Blade, Enchanted Shield, light armour, Dragonbane Gem
Similiar idea, the Piranha blade is great against Ogres as it will chew through their multiple wounds faster. Again, 2+ armour save, and 2+ ward against flaming attacks (background wise, he's the twin that was spawned with the first guy, helped him take down a wounded drake that attacked their city).
Skink Priest
Level 2 - 35
Engine of the Gods - 290
Good stuff. Have you considered taking Plaque of Tepok (one extra spell could come in handy), or maybe a dispell scroll? The former is if you actually plan to use his magic (he could always roll Comet, you never know), the second option is more useful as Purple Sun and Dwellers are going to be spammed into your guys (so you'll at least block the successful attempts). Don't forget to hide him behind your Temple Guard+Slann block and keep popping off the ward save ability.
Don't need a champion, musician is good. Standard Bearer should take Razor Standard, it will make them a lot more effective in combat (especially when stacked with the Eternal Flame banner on your Slann). We are one of the few armies who will be able to pull off that combo, as normally heroes can't take anything else if they take a banner.
Saurus Warriors (20) 5x4
FC
Drop champion, add in Scar Veteran to fill it back up to 20 strong.
Saurus Warriors (30) 6x5
FC
Spears
Drop champion and spears. I'm really not sold on the idea of spears, simply because of the penalties it induces for not much benefit. You miss out on that free 6+ ward from the shield parry, and in combat you also go down to your 5+ skin (as you can't use shield in conjunction with spear). So, it's either a handful more attacks vs free ward saves/better armour saves in combat.
Blowpipes I assume? No need to take more than the minimum, 10 is all you need.
Chameleon Skinks (6)
Brave
Good choice, although Brave is a waste of points. No need to take more than 5, they're going to die horribly after they're done sniping a warmachine crew.
Might want another unit of these guys, they're that good. Remember to play 'Trogdor' when using them, for added hilarity.
Always fun, although kinda one-use.
If you need the points elsewhere, I'd drop him. The only Ancient Steg I have is the Engine of the Gods. They're not bad, they're just squishy against war-machines. Especially the Skink crew.