Here are my thoughts....(borrowed from a post I found and modified)
Thunder Lizard = 1400pts (not including weapons)
M WS BS S T W I A LD
8 5 0 10 8 10 1 6 5 (*9 Slann Driver)
Type:
Monsterious Creature
Special Rules:
* Slann Driver (Must have a Slann driver, This Slann can only cast 1 speel and can not cast any offensive spells since he must concentrate completely on keeping the Thunder Lizard under control.)
* 6D6 + 1 Impact Hits
* 2+ Scaly Skin Save
* Terror
* Devastating Charge
* Large Target
* Multiple Wounds (D6)
* Cold Blooded
* Unbreakable
* Thunder Stomp
* Uncontrollable
* Trample Terrain
* Massive
* I Think you made it mad!
* Thick Hide
* Trample, Stomp...
* Thunder Roar
* Siege Tower
Uncontrollable: If the driver is killed, At the begging of every Lizardmen turn, the Thunder Lizard must take a leadership test. If it is passed you control the beast as normal. If it is failed the beast breaks free of its control and charges the nearest visible unit (friend or foe!). Next turn you roll a D6 to attempt to regain control. For each spell caster you have you can reduce the target number by 1 (if you do so they can not cast magic this round) Now roll a D6, 1-3 you have failed to regain control and it continues its rampage. 4-6 and you have successfully regained control. If you failed then it must once again charge the nearest visible unit and next turn you must attempt to regain control only this time on 5+ and it decreases every turn it stays out of control until it reaches 7+. It has gone beyond all reach and it remains out of control for the rest of the game.
Massive: The thought of killing something this gargantuan with a single blow is laughable. The Thunder Lizard is immune to Killing Blow and Heroic Killing Blow. Also subtract 3 from the amount of wounds an attack would cause if it causes multiple wound, to a minimum of 1. Poisons are also less effective against the Thunder Lizard due to the amount of time it takes to travel through its bloodstream and take effect. If a poisoned attack rolls a 6 to hit it merely gains +2 to its roll to wound instead. While its size makes it harder to kill it makes it easier to see. Any shooting attacks gain +2 to hit against the Thunder Lizard.
Trample Terrain: A Thunder Lizard is capable of trampling terrain under foot as it advances across the battlefield. Terrain does not effect the Thunder Lizard. Before the game begins, decide which terrain the Thunder Lizard can crush and how easily it can. A simple forest may only be a 2+ while a fortress wall could be a 5+. If it is passed remove the piece of terrain from the board. Troops garrisoning a trampled building immediately take D6 Strength 6 hits per level of the buliding. A unit in trampled terrain merely suffers D3 strength 3 hits.
I think you made it mad…: If an uncontrolled Thunder Lizard suffers an unsaved wounds from a shooting attack it immediately moves D3 inches towards the unit that caused it.
Thick Hide: Even if you pierce the Thunder Lizard’s scales there is still a chance that you won’t cut deep enough to do damage. A Thunder Lizard has a 5+ Ward save.
DAMAGE: Damage against the Thunder Lizard is rolled as on the Stegadon hit table (crew or beast). If you roll and it hits a platform randomize the hit with a D6 there are 6 platforms so assign a number to each for the game. Specific platforms can be targeted for -2 to hit and then roll against the Stegadon d6 table to see if you hit the beast or the crew. Troops riding a Thunder Lizard are immune to psychology and do not take panic tests, they have nowhere to run!
Trample, Stomp...: The Thunder Lizard can not be stopped by units who engage it in Hand to hand Combat. A unit that attacks or is attacked by a Thunder Lizard sustains 1D6+* (* = the rank bonus of the unit being attacked) Strength 10 hits. Work out damage and saves as normal. Each turn the Thunder Lizard and continue to move on causing stomp attacks. Those models that engage the Thunder Lizard in Melee Combat will be allowed to wheel and attack the Sides of the beast for as long as it remains touching their bases. Because of the height of the Thunder Lizard all units that are in Melee with the Thunder Lizard as still able to be targeted from ranged weapons from the javelins and blow guns from the Skinks aboard.
Thunder Roar: The Thunder Lizard's roar will break all enemies in contact with it. Deafeningly loud and terrifying neither the Thunder Lizard nor any units in contact with it actually fight if they have not already done so this turn. The Thunder Lizard’s side automatically wins the combat round. The enemy must make a break test with a –1 modifier.
Siege Tower: The Mammoth is so tall that troops in the howdah can use it as a siege tower, and can exit the howdah onto castle battlements and towers as if it was a siege tower.
