This mechanic is fairly straightforward and the title basically explains it all. The point of this mechanic is to make the player feel ‘Epic’ after completing something within a game. This can range from anything such as defeating a boss to coming first in a leaderboard.
A good example of a game that does this is Star Wars: The Old Republic. Each World of the game has what is known as a ‘World Boss’ which is essentially the hardest enemy on that planet. These bosses usually take more than one person t defeat and when doing so make the players feel ‘epic’ as they have completed a hard task. This mechanic even coming into play before the players have defeated the enemy as the boss spawns in random locations across the world. Therefore the player will feel ‘epic’ just for finding it.
This mechanic happens very often in shooter games such as Call of Duty. A common tactic called ‘trickshotting’ is considered the hardest thing to pull off in the game as it requires perfect positioning and timing. The trick shot is where the player jumps off of something, spins around a certain amount and then kills the enemy before they have reached the ground. Since this is a complicated move it means that when the player pulls it off they feel epic as not many other people can do this.
If I were to use this mechanic in my own game I would do it similarly to how Call of Duty does it. What I mean by this is that the players themselves would develop a tactic or maneuver that they consider hard. Which in turn makes them feel epic if they pull it off.