Cool down is a period of time when an action can't be used after it has been used. It imitates weapons / actions becoming overheated in real life requiring some time to cool down again. If, in a game, one player has had the chance to use an action against an object, which may be the game itself or another player, continuously using the action might not give sufficient time to provide a feedback to the player and / or other players to act. This can lead to poor balance and consequently deteriorated experience. Incorporating a cool down puts a cap on using that action and solves the previously mentioned problems.
Avalon: The Legend Lives
Text-based online multi-player role playing game released in October 1989 that follows closely in the tradition of early Multi-User Dungeons. It is from this game that the genre defining feature of cool down originated to give a more meaningful experience of player vs player fighting.
Resident Evil Revelations
In Resident Evil Revelations, the boss fight sequence against the Malacoda has the player fire a chain gun from a moving helicopter. The chain gun however starts to overhead and can become inoperable if the player continues to shoot. In order for the chain gun to cool down, the players needs to stop firing. This sells the experience of firing a weapon that can overheat and adds a bit of strategy to the gameplay as the player has to keep track of the heating level of the gun and decide when to fire to maximize their chance of winning.
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Need for Speed: Most Wanted
I liked how Need for Speed franchise implemented cool down in 'Most Wanted' to evade cops. Once the player loses the visual contact with police, the player can enter cool down zones and stay there until their heat level reaches zero. The player will be re-engaged into pursuit if the cops enter the pursuit circle. This gives interesting choices to the user like to either drive to new cool-down zones or wait there and monitor the cops activity. Overall, the cool-down works like a hiding spot creating an agitated experience to the player.
The League of Legends
Cool down being used in the League very well. It prevents player overpower and gives players equal chance to win the game. In the game, different action have different cool down time in order to balance the difficulty.
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Paragon
Cool downs are used in MOBA game, Paragon where a specific ultimate power of the player has a longer cooldown as compared to some basic attacks which have relatively shorter cooldown time. This gives a balanmce to the game as a player cant keep using his ultimate power continuosly to inflict more damage on the opponent. He has to now strategically use his ultimate power at the right time.
In the below image, the circled part that I have highlighted in red is the cooldown timer for that particular attack.
