So you want to be a Lord of the Underworld do you? Here's some things to get you started after playing all these games to train your Nastiness....
1. Get a suit of armor. Breastplate, helmet, leggings, armlets, gauntlets, steel boots, a red and black cape. But underneath it and before you start you'll need a black wizards robe, as you're a spellcaster before a black knight;
Purchace a Black Wizard's robe
Purchace a Medieval helmet
Purchace a suit of Medieval armor
2. Build your Dungeon Heart. Your Dungeon Heart is the source of your sorcerous power, and the container of your soul, as any experienced black mage knows to not bind your soul to some object is to pursue a mortal end. By having your soul bound to a Dungeon Heart, your body may perish, but only to be reincarnated instantly full body, near your Dungeon Heart should you fall to enemies or some accident befall you. Your Dungeon Heart should be made of blood red quartz, as the infernal energies of Hell are this color and Fire element is the realm of the soul. At first your Dungeon Heart can be small, but over time you'll want to add to it more red quartz, till it's the size of something only a decent sized infernal temple could hold. You'll need black steel to hold your Heartstone in to make a decent Dungeon Heart;
Buy your Red Quartz
An example of purchasible Black Steel
3. You'll need to collect a library of black magic, to power your underworld domain and understand the ways of the Void, Hell, the Abyss, the Chaotic planes, and your home which is partly physical (under the earth) and partly metaphysical (a place of Hell, the Abyss and the Void) The Underworld;
List of Books on Black Magic
4. Your own Underworld Grimoire. You'll be modeling your home to be like the Greek Hades, and other mythological underworlds, and so you must understand the potential landscapes past the base tunnels and dungeon rooms. Also you'll need servants and monsters to serve and guard your dungeon and protect your Dungeon Heart;
A description of the classical Underworlds
Goblins, your main servants
Imps, your secondary servants and minor monster
A collection of Monsters to summon and serve you
5. To be a minor or major Dungeon Keeper. If you are destined to be a major keeper, you'll want to purchase an old dungeon complex or a depleted mine. This will be your home, where you will live and rarely leave, only when to buy supplies from the surface world that you can't gain under the earth or via your underworld magics. Don't forget to pay your taxes for your land to the goodie goodie overworld governments, or you may have to face off against the military who are the modern equivalent of the King's Knights, powerful heroes. If you wish to be a minor keeper, than any old house or appartment will do as your mundane residence, as you'll be busy building your dungeon in the less material planes, in another dimension than the earth realm, in the voidian underworld, where the great outer gods and demon lords, and other entropic, chaotic, or spacial lords exist. You will greatly amuse them either way you keep, minor or major and be sure to build shines in your material or "astral," dungeon, to gain many boons.
Whether major or minor, you'll need to learn how to astral project, that is project your consciousness to other planes/dimensions, to weave the fabrics back and forth from your astral and physical dungeons (or purely "lower" astral dungeon, in case of minor keeper), and to your Dungeon Heart.
Astral Projection through Lucid Dreaming (powerful)
Astral Projection through Meditation
6. Additional tips and hints. Goblins are Earth Elementals also known as Gnomes, who have gone astray out of the negative attributes each element has. They work for dark sorcerers, like gnomes do for light and grey magicians, freely or for a price. They like dense energies when being feed, so be sure to study how to channel the root energies of the chakras and universe, which colors are usually reds and blacks. They also like gems and gold, silver, and copper coins as presents you can place on your altar or bury around your home or in your physical dungeon if you have one. Play all the listed games, to get ideas for monsters and rooms for your dungeon, and how an evil dungeon keeper should be. Finally make friends with other keepers, both human and unhuman and link your dungeons together by magic portals. Most of all have fun, because it's good to be evil, a paradox worth experiencing.