I would usually go into the red line if I'm not going to be using the lord for dueling such as Queek or Grimgor.
As for Tomb Kings; after uniting all the lands south of the Badlands (Except the dwarf gold expedition) I've begun heading north but I've hit a bit of a snag. The Wood Elves have expanded quite a bit and I've been having big problems actually fighting them. They out shoot me, my infantry's too slow, my constructs are big targets and my chariots are too brittle. So far I think I'm going to have to rely on Nehekhara Horsemen to chase them all down as armies of skirmishes and fast cavalry are requiring me to face each of their armies with 2 of my own. It's painful.
After many centuries of suffering under the yoke of Wood Elf tyranny, I have been able to devise a universal strategy that works for every race and faction against this blight against the world.
It's the final solution.
1. Wood Elf recruitment, income, and power all are based only in Athel Loren. It doesn't matter how many outposts they have, everything is based on Athel Loren.
2. Trying to invade Athel Loren while the elves are actually in there is suicide.
3. What you need to do is let the elves do their crazy "conquer the whole world" phase that they do after they confederate themselves.
4. Then while their 4 or 5 stacks are out conquering say... Norsca, you sweep in with two fullstacks of as much arty and heavy armour troops you can get.
5. This is because they are weighted really heavily in autoresolve.
6. Then you burn the undefended Athel Loren to the ground.
7. GG NO RE no more Wood Elf problem.
Also they're pretty trash at sieging you, so as long as you sit behind your walls you should be relatively okay. Just know they'll snipe all your units defending the walls.
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I swear fighting against the AI as Wood Elves is the worst. Their micro is insane with that faction. It's not that they're impossible to beat, but rather every fight takes so long and you lose so many units. It's a true battle of attrition.
If you actually want to fight them mano-a-mano, then from my experience cavalry is not the answer (unless it's like dogs or Beastmen or something, which are hyperspeed fast). If cavalry was the answer then Bretonnia would have a super easy time against WE. On the contrary they are awful against them.
I found the best answer is to fight them with ranged units. Yes, it sounds patently stupid, but the only thing the AI can't do with Wood Elf micro is it doesn't know how to focus fire its units. So I found the best way to actually fight them is to group as many ranged units as I can spare and snipe all their ranged, while having my melee troops hold off theirs. No need to chase them all over the map.