[Illuminated One]

Well, some ideas hope they help.


Thugs and SCs

Well, I think Ballz guides covered that quite nicely. To recap, what you want ideally is to take no damage at all. A human swordsman deals between 10 and 22 damage so anything with 25 prot should be save (not against giant nations or other thugs, though). That is if he doesn't get fatigue. Same goes for other things like defense, awe or somesuch, but that's more complicated.
And you want to deal enough damage to kill everyone, so brands are often taken (area damage).


Tarts

Some can Cloud Trapeze + Rain of Stones (death to all communion nations)
Some can Master Enslave iirc
Some can cast Acid Storm
Well, normal mages can do that too, but they usually kick the bucket after (insert applicable battlefield spell here).
Those that have all slots usually make good SCs (Fire Brand, Charcoal Shield, Elemental Armor, some helmet, antimagic amulet, ring of regen as some idea what you can give them).

Globals

Well, most notable are the gem generating ones, like well of misery. Everyone likes extra gems.

The other ones (like the admirals army) are hardly worth it imo unless if you have some funny strategy with them, they can be quite good. For example Enchanted Forest is extremely cheap in CBM, and will result in a neverending stream of vinemen. These are not very good in combat and will die in droves but since they are practically for free who cares?
The things is as with everything else you'd have to look for synergies.
Marverni has very good but frail long range mages (able to cast army of gold and battle fortune at the start of the battle, if applicable also elemental resistance, regen, etc) and ok troops that have a morale problem. You just use them as a meatshield that takes a while to hack through while your mages decimate your opponent from the back.
Every 40 vineman are another druid (since you just bought 30 warriors less) and they don't run from the field leaving your exhausted mages to die.
Another example - haunted forest. Every unit that is killed is instantly reanimated as a sleep vine beasty. Sleep vines cause fatigue damage which can be the death of any elite that doesn't pass the mr check on a regular basis. Now who'd like that? Niefel with their 1 man armies? Or Machaka who can get 100 militia out of the next best fort any instant and they still all die?
I don't know if they work against undead, there are so many caveats (for example, vine men can't be reanimated as undead or vine beasts... d'oh) in the game that you can't know them before you actually have used them. If you don't want to be surprised in a MP game you have to run tests yourself.

Otoh there is a reason why the common late game strategies (blood and tartarians) are common. Thinking your new strategy is so powerful that you can live without them is most likely a mistake.

There are also the extremely powerful globals:
Arcane Nexus ... what a Seraph costs only 100 pearls? (well, you don't actually use the pearls you wish for gems and make tartarians...)
The Forge ... forging for cheap. 50 item lab limit sucks
Utterdark ... everyone is broke and everyone is blind but you (well, if you are you did something wrong ... demons and undead ignore darkness or even grow stronger)
Astral Corruption - never seen it but it sounds fun
These either kill you (through gangrape) or win the game.

Blood

Well, firstly it's massable and reliable. The only limit to your income is the number of provinces you can hunt without killing population.
Another thing is you don't get blood in exchange for gems but in addition to them.
Resummoning an air queen is a lot more painful than loosing a demon lord, since your air gems are in demand for items, too, and your income is hardly as high as her cost. A late game blood nation can summon a unique every turn. And there are also a lot of unlimited summons besides the uniques, with only tartarians to keep the balance.
And then you have some extremely powerful spells to dispose of enemy SCs.