Event matches are special challenges that were first introduced as a set of 51 single player tasks in Super Smash Bros. Melee. Each event match puts the player into a scenario with special conditions and a certain objective. The player must complete the objective in order to complete the event match, and the game records the completion and "score" of each event match. A completely new set of 41 single player event matches was included in Super Smash Bros. Brawl, and, additionally, a separate set of 21 co-op event matches was introduced. Brawl also introduced three difficulty levels for each event match - easy, medium and hard.
Most Melee events allow the player to choose any character, with relatively few being pre-determined (those are 21 pre-determined Melee events). This is reversed in Brawl, as every event except the few All-Star Matches and final events have set characters.
In Super Smash Bros. for Wii U, there are 55 single player event matches and 21 co-op event matches.