1st thing - units of 20 warhounds are too big. They are deployment drops so make them into units of 5, unless you want to go hunting, then 8 or 10. 20 will be unwieldy to move, and 10 will have nothing to do. So at least break them up.
2nd - you have literally no infantry blocks, and while I understand it is a fast list, with nothing to break steadfast, I can see some trouble.
Also the lord is kind of hard to read. So it is a lord with the mark or tzeentch, mounted on a manticore with iron hard skin, and he has the gifts soul feeder, 3rd eye of tzeentch, and flame breath, a shield and halberd for mundane gear and for magical items the helm of many eyes and the talisman of preservation? If so I would say he is good. Drop the shield. You can't use it in combat anyways. Flame breath maybe is worth keeping, but dropping it for the armour of fortune (the one that gives the 4+ ward, I think that is the name), the dawnstone and scaled skin would make him more survivable. 1+ rerollable armour save, 3++ ward save rerolling ones, with 5 ASF s6 attacks + manticore. But he is good as is too.
Chariots are OK.
The marauder horsemen look good, but maybe invest in light armour for that 5+?
The gorebeast chariots are OK, but I don't think they are too much better then core chariots.
The chimeras look good. I am going to be getting a few of those models soon (coincidentally, looks like it is made off of the manticore kit with slight head and tail changes). I don't know if I'd take breath, but it is up to you, and regeneration is awesome.
I don't know about the shaggoth. I probably won't run him, but if you try it out can you tell me how it goes? I want to see if he is worth it now.
But it sounds like a fun list. Have fun with the new warriors and good luck!