pDoomy is good for infantry lists, which makes him great at supporting your fennblades, which seems to be your main unit.
One immediate suggestion I have is the Krielstone
UA. Being immune to continuous effects will prove invaluable against your meta, since that is a huge strategy employed by Menoth and Cryx. If you're playing an army other than that then you can always use +1
str (stacked on top of say the mauler's animus if on a beast hehe), and that increase in strength can place any infantry from average to above average and be enough to wound harder armor. I would suggest making the KSB unit full size with Doomy. He has the fury to spare and you'll need to increase the range of the aura if your
CC units and beasts go too far (which tends to happen if you want to activate the KSB first for +1
str).
I used to use the chronicler as an auto include, but now I hardly ever use him. In your army he seems more viable, giving your fennblades concealment on the way up and knocking down counterattackers. His Charge of the Trolls would be great if you used the impalers behind the fennblades, but in the list you have I don't think impalers are that great. They are usually better for locks with ranged for the animus, and as a pincusion for damage transfer otherwise (although I love using their P+S 13 boosted shot to slam models at range... I actually haven't yet played a game where I didn't bring two of them).
Having your two maulers isn't a bad way to go. I personally use one every game and is my favorite beast in the game (his model is the reason why I started playing trolls in the first place!). His animus is one of the best in the game. He has an awesome chain attack. He has a high threshold. With the KSB he has a very high armor and he can heal. The axer only makes him better (although you can't have both animi at once, which is a bummer).
I'd really really highly super suggest taking whelps whenever possible. Getting rid of unwanted fury helps trolls achieve insane damage output, especially when fielding two maulers. Nothing gives an opponent a smack to morale like loading up two maulers to 10 fury and not having to take a threshold check the next turn. Just keep them off the table and if the beast is damaged in
CC place them within 1" of the model in
CC to give annoyance, while still being in range for comfort food. Either they get -1 to hit you or they smack the 0.4 point model. Either way is good for you.
Your current list isn't too shabby for a
TAC. Just watch out for assassinations since doomy is already prone to that, let alone having a whole aggressive army leaving him behind without a bouncer. Your Circle/Legion/Cryx opponents will find a gap in your line and send a heat seeking missle toward him. With so many aggressive beasts you will most likely be out of fury to cast animi and can't transfer damage, and doomy doesn't have a scroll like Madrak does.
When you expand this army I highly suggest using eDoomy with Mulg and at least one Mauler or EBDT with an Axer. Janissa too. Do what you want with the rest of the points and you'll be fine

.