Kameo Fighters are a gameplay mechanic introduced in Mortal Kombat 1. Kameo Fighters act as an assist system in the game, allowing for offensive and defensive capabilities depending on the Kameo Fighter selected.
Overview
From a separate roster of fighters, players are able to choose from an additional character that can be called into the fight to assist the player. These fighters work in a similar fashion to assisted fighters in both Injustice 2 and Mortal Kombat 11, both in the Multiverse and Towers of Time, respectively, in which a physical fighter can appear on the fightline and perform an attack on the opponent while the player is attacking the opponent, defending against them, or otherwise attempts to start up a combo attack. Kameo Fighters replace interactables used in previous games.
Most Kameo Fighters are notable for having their debut appearances, unlike the main roster. Additionally, Kameo Fighters can perform their own Fatalities and Brutalities for whoever fighter they assist. Many of the Kameos' Fatalities are taken directly from their klassic Fatalities, though some Kameos do have a Fatality never seen before. Each Kameo has 2 Brutalities each, with the exception of Darrius and, technically, Shujinko.
Kameo Fighters are also used for Breakers and Fatal Blows, having been integrated into the latter. Whenever a Fatal Blow is performed, Kameos will perform the first part of the special attack before the fighters they assist finish the attack on their own. Because of this, Breakers and Fatal Blows cannot be performed if no Kameo is included, such as seen in the game's Story Mode. But if the Kameo paired with the player is not normally selectable, a modified version of that character's Fatal Blow will be performed before the player's character does their usual Fatal Blow.