[Baalz]

Vanheim vs darkness you want to cultivate your blood economy (if you haven't). Vamp lords will get you some pretty decent D muscle - wither bones, wither bones, reinvig, wither bones, wither bones. Get 3-4 of the immortal guys and that's a whole lot of damage at the cost of 1 blood slave for reinvig. Army of gold, anti magic and darkness won't help a lick.

Summon some storm demons. They'll blast lightning damage and won't care about darkness (they may not care about storms because they've got stormpower, don't remember if that impacts precision). Sounds like you're in pretty late game so get a guy or two up who can cast infernal tempest. If you can cast that a couple times per turn and are looking at having 60+ relatively high precision lightning guys who don't care about pretty much anything other than lightning immunity. They've also got darkvision, magic AN weapons, etherealness and a good defense so once you slap a buff or two of your own on them (army of lead yourself) and they should decimate Umbrals/trolls under darkness (in fact, you probably want to use your vamp lords to put up darkness yourself when the trolls come out.

Trolls & umbrals are both large with bleh attack, so imps will tie them up pretty effectively. Slap a couple lifelong protections on your commanders and the high defense darkvisioned little buggers will keep them busy while you blast to your heart's content.

Now, assuming you've got no blood economy set up as you haven't mentioned it(big mistake! Vanheim should be a blood nation!) I'd look at stuff that doesn't require precision. Wrathful skies will comfortably ignore everything you've mentioned so far, just make sure whatever you're fielding can handle it. Put it up and let them guard commander all they want inside the walls. If their mages are all pretty squishy you could drop a few rain of stones via dwarf if thats an option. If you've got a decent W mage (no idea what your resources are) wolven winter is really, really nasty to cold blooded casters and you can combo it with grip of winter for the storming (again, prepare your own troops for it). Won't do anything to the umbrals, but it'll lobotomize their support.