Oh well, I clearly recommend you to eliminate lair which get too annoying to avoid being overwhelmed
I wanted to do so, but it was rather hard with ghosts pooring in in the dozens, together with massive amounts of demons and serpents as well. That each lair was defended by massive hosts didn't help much either, heroes are pretty reluctant to attack 8 bears at once.
Guess I got pretty unlucky in my placements though, I couldn't even target the ghosts because my heroes didn't dare explore past the bear dens blocking the path, which kept getting harder and harder because heroes trying to go after it's flag got 8 bears and 10 ghosts to combat...
About the ice mage, They are, to my mind, weaker than the standard elemental gardian, and also they don't attack if you don't threat them.
Never got around to try them. One portal got destroyed by my heroes on it's own because they do that with portals, and got the holy site (didn't know they were related though, read that here later). However once I got my Paladins out there, the Imp Advisor and the Ogre host arrived to kill my city.
About the spawnbug, If you found more info I could check it.
Like I said, you probably can't help it, since it's an error in the way upgrades are done, which is unnoticable in the missions provided because monsters generally do not stick around their lairs to defend them, and if they do those lairs generally do not upgrade.
The bug is that when there is an upgrade done, all statistics (of the upgraded part) reset to 0/X. Meaning there are new slots for monsters around lairs to spawn and protect their lair. But the old ones still roam around too! While they do not respawn, their presence alone makes lair destruction a lot harder. Not that much an issue in the campaign as I said because the behavior is rare if used at all, but in this map creatures do roam around their lair and upgrading is more frequent. Allowing for example 8 bears to roam around a lair with a max of 4, or 20(!) ghosts for a 5 lair. See also the screenshot (that immediately shows off the ogre).
Example:
Bear dens start with 0/2. All fine. With 2/2 2 bears roam around a lair, like they should. Lair updates to 2x 0/2. Now 6 bears roam about, while the max should be 4. Once it upgrades to 2x bear and one greater bear one of the 2 resets to 0/2 again (probably the "upgrade" of that specific spawn, as the other remains 2/2). Now 8 bears and 1 greater bear roam around a 4 and 1 max lair. Same happens with several others, and this makes destruction while very late in the quest much harder.
Example for a Crypt defense:
Also I'll be very interested in one or two screen showing your lair repartitions
Day 54. Only managed to down 4 lairs so far. A dark portal, rogues guild and graveyard, all starting very close to my base, and a Serpent nest somewhat further out.
Lowest one is a dark portal, to it's left is a bear den.
Around my base are the obvious sewers. Upper right is a minotaur pyriamid. The 2 flagged at the top are a Serpent nest and bear den. Left is a Portal to Hell. Streams of undead flow out of locations I had yet to find, when this happened:
That costed me a couple of buildings before they finally got seperated enough for my heroes to kill them (damn, wish I had lightning storm).
And of course it all ended when the Imp Advisor arrived at the scene. Did however manage to finally destroy the 3 bear dens and the final serpents nest, when the "hidden" crypts starting sprewing Ogres, heavily defended by ghosts (as seen on the screen earlier):
(It may seem quiet, but that's because the waves made place for the ogres. The waves were worse, so I thought all could still end well when the Imp started killing my heroes and blowing up my buildings
, nope...)
Anyway, gonna give it another whirl now
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