Overlord

This solution is not made by me. I found it on another site. Credit goes to simalcrum who made the guide.

The Golden Hills Abyss will be in the castle courtyard (hence a good reason to
finish the core game before attempting to come into this area beforehand). It
will not appear until the Mellow Hills and Heaven's Peak Abyss are completed
and the Ruborian Desert is available. Gather gold and green minions but hold
them back at the first room; use Inferno or Combustion to get rid of the
wraith gunners then bring your minions through.

The next puzzle consists of using gold pots to lure dwarves. Kill the Wraith
reaper and take the gold with a few minions (leave the rest guarding near the
portals). Like the other abyssal puzzles, target the gold and use the right
stick to move the minions manually. Lure the dwarves to the statue of King
Goldar. After enough dwarves work on the statue, it will start to break. The
puzzle for this dungeon is clear -- kill the statue to claim the stone. Look
for more gold lures in the other two rooms and do the same. The dwarves will
not attack Overlord or minions so long as gold is being used as a lure.

Don't forget to pick up the gold shards created by the statue each time it
cracks -- they are worth a bunch of money.

Go into the side room that resembles the Mines (Slug Caves). Follow the drunk
dwarves to the stone wall. Kill what ever is on the other side, then use a
bomb to bring the wall down to move on. Use green minions to suck up the
poison, hit the switch to pop up a bomb plant. Take the bomb to destroy the
blockage at the stairs and head downstairs. Leave all but five or six minions
at the top of the stairs however. Take the gold from the slug (by killing it)
and quickly getting out of the pit. You can probably avoid fighting the big
slugs. A bridge to the Wraith reaper will appear once the gold is upstairs;
kill the reaper and its buddies. Rotate the turnstile and get back out to the
main room.

Cross the bridge and prepare to sacrifice a minion afterwards. Bomb the first
weak wall to reveal a closer bomb plant. Bomb the second weak wall with the
revealed bomb. Past the second wall, get the warp point and prepare to move a
minion with bomb past the three thorn walls. Locate the two switches to form
bridges back to the main room and go there (the second switch apparently gets
the second unique item in this dungeon). Before nearing the gold statue, max
out the horde to 50 and put in 5 blues. Take the slug gold back to the main
room and lure the dwarves there. It's a good idea to place the max horde at
the bottom of the stairs and let the dozen or so dwarves work on the statue;
you protect them from the wraiths that come in. Mount a counterattack once the
two stone giants appear; unlike the one in the Contruction Yard, you can kill
these two giants.

Go into the other room next. The room here is the "Escher Room". Hit two
switches while in the stairs area. This will let Overlord and gang cross a
chasm to a place with four minion portals. Enemies here respawn all around, so
power through quickly and get to the portals (a rest area of sorts). Make room
for two red minions in your horde and stash your minions near the arcane blood
pit. Take the reds into the room and activate the two beer tap switches
quickly. This makes the dwarves drunk enough to fight off the wraiths near the
reaper Although you can try to approach it without the beer, it's not a good
idea considering the enemies in the next room). Take the rest of the horde
(mix it up, but try to avoid greens since they jump into the lava). Chase down
the reaper, hit the switch to open the door to the reaper's residence and take
the gold.

Going back to the main room, you will need the Wraith berserker (the guy who
kills minions with his axe charge). Lure it into smashing the stone wall. Your
Overlord can do that without killing your minions if you have good
(regenerating) armor. Before moving on, get the first unique item in the
dungeon, the Armor of Fire. Locate the mana pit near the Wraith berserker;
there should be some bombs that your minions cannot reach and a stone wall
that's begging to be destroyed. Use the old stand-by Fireball to set off the
bombs and get to the first mold.

Once you get back to the main room, you need to start luring dwarves to do the
dirty work. Surprisingly, the wraith attacks are not your worry. Instead, you
need to worry about the dwarves going ape shit when you have the abyssal
stone -- the bombers and flamethrower dwarves will be the main worries, easily
killing off large sections of your horde. Defend the stone against the dwarves
and take it when the wave is over.