[Vulture]

In an all-undead army, neither the Whip nor the Dagger are a choice, mate. Only for one unit (Skellies) that is a terrible waste of slots. Any +Atk weapon greater than 3 (Dwarf hammer, Demetrius, Dragon Slayer, Equilibrium) will perform better in the long run.

Btw letting Ancient Ents tank is a terrible idea since you can't ress them.

As for the Human playthrough. Depending on if you count Sea Dogs and Marauders to them you can have a fairly decent team (Biting Strike and Fury Attack are beast) until you get to boss battles :> I'd NEVER play Warrior with humans. Ever. Reason: a Paladin can easily (!) get Bowman Commander and Onslaught. My Paladins always have so many might runes left I take Tactics 2, and Dark Commander and have still might runes left. It's not like it makes sense to take Destroyer or Chaos 3 with a Paladin, is it ? A Paladin is a warrior with more runes and less ldr and atk. A warrior can never sustain enough mana and spellpower to keep them all alive. Unless you don't care for losses and give yourself "Horde" for everything. but that's kinda pointless. Impossible isn't a challenge if you keep restocking everything. Every beginner can do that. Marauders btw only cost 30 ldr. Fairly priced for a lvl 2 unit. Compared to Priests with 50 ^^

As for the Animal/Neutral playthrough I agree on the Snakes. With Feonora and the Snake King Ring (maybe even two) you might even bring regular snakes, too (No Swamp Snakes, tho, as their damage is poison only. Royal and Snakes have physical damage. The poison is an after effect as a bonus)

As for the archer playthrough. A: it is completely impossible. You WILL be wiped on all major bossfights. And in order to not get your ass handed to you, you MUST play mage in order to Phantom + Teleport early on (which both you won't get before the Islands), else everyone will just swarm you in melee. Imagine Dragon fights, fights against Lake Flies/Fireflies, Griffins and heroes with the Lightning spell. You can't spread out 5 troops on the left part of the battlefield far enough so he would refrain from doing so or doesn't hit more than 2 of them. Also you'll always need rage before the battle to drop a Wall/Icy Thorns/Ice Orb against otherwise fast melee units with "Running".
Next problem will be the range penalty. There is no mass Dragon Arrows. Skeleton Archers and Bowmen suck donkey balls when it comes to range; 5 or 6 tiles. 5 tiles is also what many units can bridge to get into melee in one turn, the rest in 2 turns.
Elves suck in general. The leadership/dmg ratio is dreadful. You should replace them with Thorns. I don't think the Telescopic sight works with them but it doesn't matter anyway as it only works with the base Atk of the unit which is pretty much nonexistent ^^ Just like with the Bowmen and Skellies.
Next thing is that you need Cannoneers. There's no way around that. You didn't honestly suggest Goblins, did you ? Crappiest archer in game ^^ To compensate for the morale loss you have the Ale Barrel and the Elven crown. That'll bring them all down to +/- 0.

I don't want to burst your bubble there but an all-archer playthrough on impossible is... impossible.

As for the Dwarf playthrough: not impossible but you'll run out of money in the late game as you will never have first strike except in round one and only if you play Paladin or Warrior and get Onslaught early. The best initiative will be 6 with the Cannoneers. Idk but you'll get stomped in Ultrax, Demonis and the Labyrinth so much that you'll go and restock your troops after every other fight.

As for the "Outcasts": lol :> We don't have to talk about that. Not a chance. But if you urgently need to, do yourself a favor and take Human Rina over Mirabella. You'll need the init and speed, believe me :>