Usually, a balanced encounter in Dungeons and Dragons involves roughly the same number of monsters as there are players. This allows you to pressure your players as a Dungeon Master with hordes of kobolds or goblins, a roving band of Orcs, and an annoying group of bandits. The enemy might gang up on a weaker player or cause other strategic difficulties for the party to solve.
Because combat works better with the party facing a group of enemies, it can lead to encounters with your heinous villains feeling rather lackluster. This is because the party is always going to have the strategic advantage as a group since they’ll always have a full round of attacks while the Villain just has to sit there and get pummeled. It’s definitely not very EPIC.
Other Dungeon Masters try to beef up their Villains with sinister lair and legendary actions, but that’s still often not enough to provide an EPIC battle. One of my favorite content creators, Matt Colville, solves this with his Action-oriented Monsters. I have taken this as inspiration to create this system of mine, If you want to see it in action, I made a full video about it on my channel linked below!