What makes the model such a paragon apart from its stats which would rival it against most Monsters in its league. Whether it be compared to a Treeman or Star Dragon, the Kadai's natural 4+ ward and 2+ fire resistance would move it one on one way above any in its class.
M Ws Bs S T W I A LD Unbreakable Monster
9 5 3 7 6 6 5 6(+D3) 8
The rule that made people blink was its Blazing body rule which gave all non-magical attacks initially a -1 penalty to wound against it. This has been faq'd so that any wounds caused by non-magical attacks will need to be re-rolled. A contentious rule change which did little to offset its OTT invulnerability against armies with little access to magical weapons and/or majority Str 3 or 4 attacks. The change of rule does give you a slight hope of wounding it with Str3 or 4 now I suppose. Here is a graph of the percentages to be able to wound the behemoth relative to strength of attack. (Thanks to Warhammer forum)
The rule change has made it much more impervious to using combo magic on the Kadai and then attacking it. Even though it gives you a sniff at it with str 3 or 4 now, needing 6's with a re-roll. This boon will reduce the success with higher strength attacks as well as offset significantly the bell curve to wound on a lower toughness Kadai caused by magic.
How to take it down:-
At Range: Most popular and preferred choice of most armies.
1. High Strength magical missile and a stacked light banishment would be the ideal choice.
2. Leadership based wound attack. Death magic, VC leadership attacks, TK casket of souls comes to mind.
3. High strength shooting armies.
1. The normal strength of 8th edition is ranked infantry to win combat.
i. Armies with monstrous infantry that can negate it's thunderstomp can take advantage of its unstable rule.
ii. Combo magic in combat by reducing it's WS to improve success in combat for your troops and negating easy hits from the Kadai. Reducing its toughness to make it easier to wound.
2. Take advantage of it's frenzy to attack it's flanks and if you're lucky a rear charge.
3. Taking advantage of it's one obvious weakness which is it's flaming attacks. Characters with protection against flaming will be effective but just remember it's thunderstomp isn't flaming.
In short shoot, shoot and magic before you go in to finish it off unless you have monstrous infantry where you can just close. My army is a little fortunate as High Elves have good access to flaming protection and magical weapons. It still caught me a little by surprise when i first faced a Kadai but then Dragon Princes come into their own against the beast.
Hope this article has helped and if anyone has a good tactic they have used against the beast please feel free to share.