"A cube placed in the present will appear in the same position in the future. Moving a cube in the present will automatically update the location of the same cube in the future."
— Announcer, Portal Reloaded
There are many games that feature time travel, but in most of them it is purely a part of the story and doesn't factor into gameplay. It doesn't matter what you do in the past, the future either doesn't change or only changes as dictated by the story.
In some games, however, any change to the past directly alters the future in the corresponding manner. This is most frequently used as a puzzle solving mechanic. For example, moving a box in the past moves the same box in the future, potentially to a location that would otherwise be inaccessible. Or you might be able to Ret-Gone a threat in the future by destroying it in the past.
This page is purely for examples of this trope as a Game Mechanic. For non-gameplay examples* and examples in other media, see the following related tropes: Retroactive Preparation, Help Yourself in the Future, Set Right What Once Went Wrong, Make Wrong What Once Went Right
Examples:
- The Legend of Zelda:
- The Legend of Zelda: Ocarina of Time zig-zags this as part of Zelda's traditional Dual-World Gameplay, where the world of the past is the world of Young Link, and the world of the future is the world of Adult Link, seven years later. Some changes you make to the past affect the future as they are performed, like the Magic Beans you plant, while others are implied to have always happened, like playing the Song of Storms at the Windmill.
- In The Legend of Zelda: Oracle of Ages, Link changes time a little more directly than in Ocarina, because Veran's entire plan is changing the past to her benefit, and so Link's quest is generally one big Set Right What Once Went Wrong, such as saving the Maku Tree from being destroyed to prevent her from being gone in the future.
- LEGO Dimensions: The Doctor Who world has several instances of this. For example, you can travel to the past and plant a tree and when you return to the future it will have grown enough to use as a platform to bypass an obstacle. On another occasion, you can travel back to when a building is still under construction and change where a balcony gets installed
, allowing access to different rooms of the building in the future.
- In Path of Exile this is the base of the Incursion mechanic. You are offered to travel back in time to the age where a Vaal temple was being built in search of clues of its final location, but you also get the chance to change its layout by killing specific architects, who will be replaced by others who will build other temple chambers with different effects or loot, and opening passages between areas that would not be connected in the present otherwise.
- Day of the Tentacle: Hoagie, being stuck in the Independence-war-era of the US, can affect the future by replacing various items or appealing to historic characters to change their decisions. For instance urging George Washington to chop down the fake cherry tree erases it from the future and sets Laverne free since she was hanging on the aforementioned tree.
- The Dishonored 2 level "A Crack in the Slab" sees the player character stripped of their mystical powers, which are replaced by just one — the ability to travel back and forth in time between the present and the night when the Big Bad Delilah was brought back from the Void. At several points in the level, manipulating the level in the past propagates into the present (such as when cremating an infested dog corpse in the past clears out a bloodfly colony in the present), but the biggest whammy comes at the end of the level, where knocking out or killing Aramis Stilton not only swaps out the entire level in the present, but also the level after that, as well as changing a number of other details, such as giving Megan Foster back her arm and eye.
- The Sims 3 includes a couple of these for the Into The Future expansion.
- The most impactful one is changing the course of the future into either a Utopia or a Dystopia, which requires doing a series of quests from Emit Relevart to either convince the military to spray an aerosol of happiness across the town to direct society to a utopian outcome, or to work with doomsayers to turn everyone apathetic towards the environment to create the dystopian outcome. The world of the future will change to reflect its state, the utopia having giant flowers that release the same dew the happiness aerosol was made from, everyone being happy, and a permanent rainbow, while the dystopia has meteors landing constantly, trash all over the place, and people have took to eating bugs.
- In the future, there are a set of statues dedicated to Sims who did something special to set the future in its current state, such as setting fashion trends or donating a lot of lottery winnings into funding for the future. These are initially statues of either NPCs, or Sims who are generated specifically for the statue. You can follow a set of instructions for every statue to have your Sim become the new subject of that statue, which will also give them benefits when they visit the future.
- Lastly, causality can affect your descendants. For one simple example, the money you have when you travel to the future will determine the wealth of your descendants, along with certain personality traits also affecting their wealth, positively or negatively. If you return to the present and either change your net worth or traits, then upon returning, your descendants may live in a different home reflective of their new wealth value. Traits can also affect how many descendants you have, such as a Child Hater having less descendants, or possibly none at all, while a Sim who Really Gets Around is likely to have more descendants. Changing traits can therefore change how many descendants you have. Lastly, if you're in a committed relationship, your descendants will be based on you and your partner, so starting or ending such a relationship will also change your descendants, though more drastically, to the point of potentially subjecting entire sets of descendants to a Ret-Gone. (Though if you're fast enough, you can find the graves of such descendants at the future's mausoleum, which will allow them to remain around as ghosts and potentially brought back to life)
- Braid features examples of this, mainly in World 4 (where the player's movement across the X axis determines the flow of time) and World 1 (where time moves backwards for everyone except the player).
- Portal Reloaded: This is the primary new mechanic this Game Mod adds. The player can place a portal allowing them to move between the present version of a test chamber and its counterpart 20 years into the future at will. If you move a box or place a portal in the present, this will be reflected in the future.
- The Cave: This is used in the Time Traveler's section, for example by blocking water from dripping in the past you prevent some stalactites from forming in the present, and killing a dinosaur in the past creates a puddle of oil in the same location in the future.
- Achron allows for this thanks to its free form time travel. Changes to the past are propagated to the future via timewaves.
- Chrono Trigger has several spots of this, most notably sealed chests that can be opened multiple times, but only if you do it from the furthest date first.
- In Ishar 3, this mechanic is the basis of the game as the city and people you meet in the present era are determined by your actions in the different past eras you travel to. Helping a wizard go back to being human after a failed experiment when that land was just a forest will allow you to meet and get help from one of his descendants, and killing the leader of the tribe that lived there when it was only a swamp will change the layout of the city as it will be founded by another chieftain.
- A rare example that does not involve time travel happens in Persona 2, in which all rumours become reality if you spread them far enough. This is abused by both the heroes and villains to spread rumours about the past in order to get desirable outcomes in the present - such as convincing people that a shop owner was a former spy to be able to buy guns from her, or that there are mystic ruins under the city from an ancient civilization to set up cults and rituals. People's very memories and pasts change in accordance to the rumours, making it just as effective as time travel.
