Regicide

Regicide, located in Heartland, is the 20th (counting each multiple-choice level as only one, not counting bonus levels) and final level of the Dungeon Keeper 2 campaign. In it, you face King Reginald, the ruler of Harmonia, whom you must defeat in order to proceed up the path to the World Portal. Also encountered for the first (and only) time are Stone Knights, who guard the portal and its gem.
==Breakdown==
The initial challenge of this level is to build up a fighting force quickly enough to hold off the periodic attacks from the five Hero Gates located at the edges of your starting area, and eventually claim the gates when opportunity arises.  Some Salamanders located in a small lava area to the south will be helpful in achieving these ends.  A Prison and Graveyard are good things to build when you can afford them, as there will be plenty of unconscious and dying heroes to fill them.
You may want to take care to hold on to some Guards from the incoming waves of heroes, as sacrificing a Guard+Mistress combo in an Unholy Temple is the only way to obtain Black Knights in this level (and a Black Knight in turn is needed to release the level 10 Dark Angel trapped near the northwestern Hero Gate).  But if you don't manage to capture any of them, don't worry; you can obtain one by first sacrificing two Bile Demons to get a Rogue, then sacrificing the Rogue and a Dark Elf, and then casting Call to Arms on the temple pool.
Once the northeastern-most Hero Gate is claimed, a Sight of Evil spell will reveal some small spots of Lair slightly to the north.  Build a Stone Bridge north from this area across the lava to find some Hero-claimed land leading to a gem seam.  After defeating a pack of Giants who guard the seam, your money concerns will be over.
To release the aforementioned Dark Angel, first build a 5x5 Unholy Temple in the 5x5 area surrounded by solid rock to the immediate east of where he is trapped (you can see him with Sight of Evil).  Then, in this pool, sacrifice a Firefly, a Black Knight, and a Warlock in rapid succession, in that order.  If you have done it correctly, then the western wall of the Unholy Temple will open up, and as soon as your Imps go in to claim the land, the Mentor will tell you about Zachariah (the Elite Dark Angel), even though this is just a normal level 10 Dark Angel with a different name. Bear in mind that you only get one Firefly in this level, so make sure you don't lose him!
After you have claimed the five Hero Gates, secured the gem seam, and taken measures to keep your creatures from wandering too close to the enemy traps, you can take as much time as you need to recruit and train an army sufficient to storm King Reginald's keep.
Remember: Creatures that you obtain by sacrifice combos do not count toward your Portal recruitment limit! As long as you have enough Bile Demons, Dark Elves, and Mistresses (or Salamanders) coming through your Portals, you can produce an effectively unlimited supply of Black Knights.
After you have defeated the King and his entourage, save up your mana, because you will need to Summon Horny to defeat the Stone Knights to the north. Don't wait too long to defeat them, though, or large waves of level 10 heroes will begin coming out of the gates just outside their door!