Okay, let's see if I can keep this straight because honestly, the power-ups come fast and furious. The signature thing is obviously the Shadow Extraction. Jin-woo—sorry, Cheol, I keep using the manhwa name—can raise the shadows of defeated enemies as his undead soldiers. They're called Shadow Soldiers. This starts with Igris, that first knight boss, and just snowballs. He gets an entire army.
But it's not just summoning. The shadows retain their skills, so he's got tanks, assassins, mages, the whole RPG party inside his shadow. The Monarch's Dominion lets him command them with flawless tactical control. He also gets insane physical stats, Monarch's Domain which is basically a pocket dimension he controls, and later, Ruler's Authority for force manipulation.
What's unique is the system-based growth. It's not just 'he gets stronger.' He gets quests, a stat window, a literal shop. The necromancy-plus-gamer-interface combo is the real kicker. Watching his army grow from one grunt to legions was half the fun, more satisfying than any solo strength boost.
By the end, he's practically a one-man sovereign, turning the tide of wars with his personal undead legion. The whole 'Army of One' theme got literal.