Resources like Gold and Life Force (the "currency" used to spawn minions) are vital for upgrading your and gear.
Once a hero is defeated in the base game, an Abyss Portal opens in their respective realm. These are challenging endgame dungeons where you must banish the former rulers to their personal hells. overlord-raising-hell-gog
Stealth specialists. They are immune to poison and can jump on enemies' backs for massive backstab damage. Resources like Gold and Life Force (the "currency"