[Mossy Toes]

Tyranids with the Paroxysm power have been very good, since they can make maulerfiends bad (or even literally useless) through invisibility.

Graaah, the fact that it isn't "to a minimum of 1" really grinds my gears--especially with all the Slaaneshi Daemons stuff that is to a minimum of 1.

Some thoughts on the list--some non-conventional stuff, but it definitely looks like it would function together. No Spell Familiar on the Warlord?

And, uh, wow. That is a lot of Termis. How do you like that distribution of weapons? I'd go for chainfists just to give those powerfists a bit more of a kick vs vehicles, but... hey, get Invisibility on those and they'll be damned tough to get through. Join one of the sorcs to them and they'll get a better DTW bonus against Paroxysm and the like... though I assume you're DSing them in, so the Sorc would have to be in Termi armor and could only be a sorc who hasn't rolled useful Telepathy powers.

Since you ask, I think it is worth buying an invuln for the sorcs. Not SoC or AoDG--Termi armor. Not even if they're joining the big Termi squad, just that it costs much less on a Sorc, who doesn't have to pay the points for a power weapon when they already have a force weapon, than on a Lord who has to buy a power weapon in the bundle. You get a better save and an invuln to boot. Though you do lose a CC attack, so one less chance to Force that Hive Tyrant to death...

Hmmm. You're considering upgrading the Herald to a MC, and need a guaranteed Invisibility? Can I recommend Be'lakor? He's a lot of points, but... hell, he's a guaranteed Invisibility and Shrouding, since he knows all the Telepathy table, and has shrouded automatically himself (for a 2+ jink cover save!). You'd have to find about 250 points above and beyond the Herald... hmm, he'd basically replace a Maulerfiend as an assaulty unit, and you could also drop 3 Termis (including a Reaper)? Such a drop would also let you repurpose 2 of the Termis as those Sorcs in Termi armor I was mentioning...

If not Be'lakor, at least get an Exalted Reward on that Herald, so you can Grimoire one of your Daemon Engines--another layer of impenetrable defense! (except when it backfires, but vehicles are already tough to kill for a reason, so a Grimoire backfire hurts them rather less than a block of T3 models)

 

[Mossy Toes]

Which I don't really know how to do. What do you think of Nurglings instead of Daemonettes?

If you don't have a Herald, go right ahead! Nurglings are the Daemons version of Cultists, especially now in 7e that they can score: basically a sort of Troop Spackle to fill in the gaps of your list. Not to mention that they can infiltrate (though, also, are a very easy First Blood if you're not careful).

Disproportionate plasma and maybe a few meltas would probably be the way I'd go, I agree. Dunno how I'd do power weapons in so large a squad: in my 4 or 5 man Termi Squads I've generally gone 1 or 2 chainfists, 2 power axes, and a pair of 2LCs. Nice to see the thoughts of somebody who's been running a large blob of them.

If you need anti-flyer to take on Nid flyers, honestly, a Slaaneshi daemon prince might be the better option for you. Take 2 greater rewards and swap the worse of them (say, the armor when you already have a 3+, or that lance/beam thing) for Lash. Meanwhile, with straight Telepathy powers, you should also get Psychic Shriek: 2D6 S6 shots plus Psychic Shriek might well take out a Harpy/Crone, and could do a decent number of wounds on a Tyrant. Shriek would be less effective, sure, against Ld10 and a Flyrant's good DTW roll, but... still, you have a pretty good anti-FMC unit, there. Just try to make sure they don't get the jump on you, because you'll splatter to twin-linked Deathspitters pretty easily too! With ML 3, that Prince would cost you about the same as Be'lakor, and would only be a 50% shot at an Invisibility rather than a guarantee, but as far as AA goes, it's one of the better options for Daemons. You don't even have to try for the combo with Iron Arm (S9 Lash, mmmm), since you're going against an FMC you can Psychic Shriek rather than trying to hit flyer armor. Though... wounding on 2+ would be nice.

Grimoire... does tend to backfire, if you don't pack along the 300 point "reliability" tax that is Fateweaver. When you really don't want it to. It can be an immense boon, but is by no means reliable, so you are right to be wary.

 

[Mossy Toes]

Whew, there is not a spare ounce of fat on that list. In fact, its ribs are showing pretty sharply beneath its skin, and could definitely use another 150 points of padding easily--but I like it. It's lean because it pushes the limits of its points to accomplish things it rightly shouldn't be able to, at such a points level. Another vehicle should make enemy AT guns more overwhelmed by your walkers, and 10 Daemonettes are far outweighed on the threat scale by the DP... though I do have to say the lack of armor on the DP makes me a bit wary. Even if he's swooping, against an enemy Flyrant, Deathspitters will be getting 11ish hits on him, 5-6ish wounds--you want to be able to take a 3+ against that.

I just wish that you could get a chainfist/power fist into the Termis somehow. Could it be worth dropping... the non-termi Spell Familiar*? The IoV? These choices are like teeth-pulling.