Chronic Logic

Arcane warrior definitely does not do that.  I hoped that it did, but it just attacked one enemy.

I don't think we need a whole lot of them, but I like the giant spider concept and I really like the sanctum tiles where spirits/undead units cannot enter them.  I think it would be too specific of a function to have an ability that just removes the special effects of a tile, and so far 2 of the 3 abilities are self-clearing (walls can be destroyed, webs can be walked in to remove them).  So, I think the sanctum tiles should probably just destroy the unit that entered and then clear themselves.

Oh, and while I like the giant spider idea, I think it might be more interesting if it weren't a 3x3 block of webs.  I think it would be more tactically-challenging to have it drop webs in the squares it moves out of.  Perhaps it would have a couple jumping actions where it drops webs through all the tiles it crossed, stunning things in that area (like the elephant tramples).  Its attack might just be very weak but poisons, giving it the opportunity to avoid enemies with webs while the poison kills them.

By and large, I find player units do a whole lot more of the killing than AI units do.  Unless the functions representing the probability to gain the abilities were different for each side, the player would end up benefiting from this change, and the AI probably wouldn't.  I think I'd be happier if the gold-bordered enemies were just rarer than if they popped up during play.

Also, I don't like the idea of random effects happening once things are deployed.  I like being able to understand what my opponents are capable of and acting on that knowledge is where skill enters the game.  If an enemy suddenly develops an extra movement range while it advances on me, and in doing so kills some critical front-liner that was otherwise out of reach, I'd be disappointed that the game made my otherwise viable strategy invalid for a reason that's uncontrollable for me.

Clockwork: +1 armor (at least), unit made inorganic, +2 hp?
  Despite being a fairly simple change that a player can make to anything with an artificer, this is a deadly ability because priests, changelings and dracoliches are the best way of approaching the super-charged other enemy units.  It definitely changes the way you have to think about stopping the unit, especially since there's no guarantee that it will be slow like all default inorganic units are.

Vampiric: All damage dealt is added to HP
  Oh god... I saw this first with a vampiric warlock.  I lost before he attacked, but that sounds horrifying.  This is an excellent incentive to focus on an enemy without making that enemy impossible to beat.

I like the shield maiden as she is, but it seems like she would be a prime candidate for an ability like this.  If she could make a linked unit next to her immune to ranged abilities.  The infantry unit could be "Phalanx" or "Hoplite" and the immunity would be derived from a tower shield.

I definitely prefer the way it is now to the way it was when it just started with upgrades for units.  I kind of wish I weren't at an AI level that didn't give EVERYTHING an ability.  I definitely would prefer it if the special abilities were somewhat rarer, but it could just be due to that AI level.

That aside, I will confine further comments as reactions to specific abilities gained by AI units:

Ascendant: +1 action, +4 hp (max 9), +2 armor (max 2)
  This ability, while strong, flags out a paragon of an enemy.  If it weren't the case that every enemy might be ascendant (what are we, fighting an army of gods?), then it would be an excellent ability.

Longshanks: +2 hp (max 9), +1 extra instance of the unit's move ability at 1 greater range
  Very clever.  I like it, except that it makes some units COMPLETELY silly.  A longshanks elephant can deploy and, in the very next turn, take your castle.  However, the AI does not use this capacity.  Not sure why.

Arcane: power is higher of normal or 5, gains attack anywhere within 5 attack for 1 action
  Making everyone into a warlock serves to make warlocks that much less interesting.  I don't like the idea of making something capable of attacking anywhere on the map, and Arcane Knights, Riders, Cavalry, Mounted Archers, Elephants and Dragons can do this.  Furthermore, having 3-action units with this ability is not fair.  I think a good change to it might be the ability to increase the range of the unit's attack by 1, or, to add a range 2 fireball to the unit instead of what it does now.

Cunning: +1 action, +1 hp (max 9), +1 armor (max 2)
  This is a good ability, but not overwhelming.  I wish things had to pay more for extra actions, but in the face of the other abilities, this isn't quite as scary.

Resilient: +3 hp, +1 armor
  Well-designed.  The +3 hp on this one doesn't seem to have the standard cap at 9, seeing as I've seen Resilient Elephants at 10 hp.

Mighty: +1 power
  Underwhelming.

I see that AI units now have little upgrades (or, in many cases, not so little) that increase all of their statistics.  I understand the difficulty incentive which would inspire this course of action, but I disagree with the method of implementation used to approach this goal.  I'm perfectly willing to accept that sometimes I'll be facing a heroic enemy who has a greater capacity for harm than a typical enemy.  However, the way it has been done now, where each stat has a chance of being increased makes armies that focus on dealing damage totally obsolete in the face of 15 hp units with 2 armor that insta-gib anything they touch.  The changes made force the approach to AI opponents to be either priests or changelings so that the non-AI player can steal these very powerful units.

As a tactical game, any development that reduces the overall tactical flexibility of the game is a bad one.  Plus, should a player decide to use a unit that steals enemy units, the game is not more difficult.  A player can more easily use the insanely powerful enemy units than can the computer.

Since I like the idea of heroic enemies, and since the AI does need a little boost, I think a more purposeful and less random step is more appropriate here than the mish-mash of super-enemies.  Heroic enemies might have a special badge icon in the corner of their box, or receive a gold outline or something.  They should be much more rare than the upgraded enemies are currently.  Most importantly, I think they should have a theme to the boosts they get.  By having thematic boosts, some combinations can be avoided that make the game essentially impossible for non-stealing armies.  A heroic enemy could have one or two abilities drawn from a logical list, such as the following:

Tough:  +3 hp
Heavy: 2 armor (or 3 armor for something that already has 2)
Strong: +2 power
Mighty: +1 power/+1 hp
Fast: +1 action/-1 hp/-1 armor
Mechanical: As though starting with artificer mechanize ability used on it.
Flying: As though starting with wizard's levitate/fly ability used on it.
Regenerating: Fully restores HP at the end of the turn (ala Hydra)
Agile: +1 dodge (ala Rogue/Scout)
Masterful: +1 parry (ala Swordsman)
Epic: Each kill grants +1 action (ala Warrior)

I would very strongly discourage allowing too many of these to mix together, or you end up with something that's just not possible to oppose OR something that trivializes the rest of the opposition because it can be stolen.  It seems to me that only allowing ONE of these abilities per heroic opponent would be wise.  It might be wise to make the unit lose its heroic ability when the computer loses control of the unit.

Pros:
More diversity of enemies, and they're more difficult.
Modified enemies are CLEARLY visible via a badge or border.
Damage-based strategies are still viable, since enemies cannot just ignore hits with vast pools of hitpoints.
The types of enemies don't converge as much as they do now, where bowmen and crossbowmen have essentially the same hp, armor, and damage.  It retains the individuality of each kind of unit.

Cons:
It might not be quite the difficulty boost that people want.