On-the-fly character switching is a term that refers to a gameplay mechanic in games in which the player may actively switch control from one character to another at the touch of a button. Games in genres ranging from action titles to RPGs and puzzle games feature this mechanic in one form or another. The specific reasons that the player is asked to switch characters varies greatly from game to game, and while some require it as a core necessity to progress, other games do not specifically require using it and may be completed while only rarely switching control to another character, if ever.
(Note: For the purposes of this concept's definition and description, this does not apply to player-switching in team sports games.)
The Lost Vikings
The Lost Vikings is a puzzle-platformer in which the player takes control of three vikings, each with their own unique abilities. Baleog the Fierce is able to use a sword and bow to attack and defeat enemies. His bow can also be used to trigger distant switches. Erik the Swift is the fastest and can run, as well as jump. When he runs at full speed, he can bash through certain obstacles with his helmet. Olaf the Stout carries a shield that can defend against enemy attacks, can be angled upward as a platform for Erik, or can be used as a glider. The player must swap between control of the three vikings in order to solve puzzles and advance from one stage to the next.
Secret of Mana
In Secret of Mana, the player eventually controls a part of three characters; a boy that excels at physical attacks, a girl capable of using healing and protective magic, and a sprite capable of using offensive magic. The player can swap between control of all three at any time. When not under the player's direct control, the other characters are controlled by AI and their level of aggression can be customized by the player. However, even when not under the player's direct control, the player can call for characters to use spells or items through the game's menu system.
Maniac Mansion is a point-and-click adventure developed by Lucasarts in which the player controls a party of three teenagers that much explore a mansion while avoiding its myriad dangers. The player can only control one character at a time, but can swap between the three on the fly using the game's menu interface. It is also possible for individual characters to be killed, and the player may complete the game with less than the full party remaining.
Resident Evil Zero
Resident Evil Zero marks a slight departure in the gameplay of the Resident Evil series by requiring the player to swap control between two characters: Rebecca Chambers and Billy Cohen. The game features puzzles that require controlling both characters to solve, and the player must swap back and forth between the two in order to progress.