He's all about stacking as many buffs onto him as possible. With the right command traits, seraphon rules, and command abilities he gets a ton of attacks.
First take thunder lizards, giving -1 to damage to keep him alive and a bonus jaw attack on the steg. Then make him your general to give him the Prime Warbeast command trait, adding +1 to attacks of the mount (including the bow unless they FAQ'd that. If you want to put an artifact on him I recommend the amulet of destiny for a 5+ ward or the cloak of feathers to make him -1 to hit, move 12", and fly. Now for in game buffs.
The great drake constellation on him gives +1 to all attacks on the model until the next turn, put herald of the old ones from the skink priest on him for net +1 to hit on all attacks, there's more than enough save stacking in our army to get him to 3+ save ignoring -2 rend if you stack it enough, and then in close combat when you charge use his own command ability on himself to grant him +1 on all attacks.
So with all these boosts, he's getting +3 horn and stomp attacks, +4 jaw attacks, and +2 spear attacks for the chief. You can triple your jaw attacks from base warscroll, gain almost as many horn attacks, and at full health 8 stomp attacks. With +1 to hit from priest you're looking at 14 attacks 2+/3+ -1 2 damage which is powerful, but then also 5 horn attacks 2+/3+ -1 4 damage at full health which can be terrifying. Not to mention the rider getting 5 attacks at 2+/3+ -1 1 damage which can finish off something. That's 24 attacks on a single model rolling 2+/3+ -1 rend. This doesn't account for monster actions to stomp as well as the charge giving a possible additional 2d3 mortal wounds. You can even cast hand of glory on him and have him reroll 1s to hit. I'm not even accounting for the bow shooting which is also scary.
Once he starts taking damage and his horn damage goes down he gets a little less scary, but it's up to you if you want to command ability him to full bracket or gain the extra attacks. On paper he's has down the biggest beat stick in our army but it call comes from the amount of buffs, as our army is super buff dependent. It's a lot easier to buff the steg and keep him around compared to a carno in my opinion.
The army I'm running now typically has him a skink priest and an endless spell, or exchange that for gotrek, but with how suped up the chief can get he just feels like a lot more fun sometimes. To see him shine you want to use a skink priest's buffs, along with the starseer and starpriest. Taking into account all the different skink buffs he becomes even scarier. I would just recommend against ramming him into high armor save targets, only -1 rend on all attacks won't do much, Control fate on the starseer on your target will help but that doesn't always go off.
Hope this helps!
