Entities have the ability to destroy other entities in the game world. When an entity is removed, it ceases to exist in the game world, but the removal or absence of the entity may affect the game world. Removal is the opposite of creation.
Collision (two or more entities occupying the same space) is the most common way entities can remove each other in games. In some games, entities have the equal chance to remove each other. In these cases, simple collision does not cause removal. The entities must be in specific states (ie, Double Dragon, one fighter must be punching another fighter), or the collision is mediated through a third entity (ie, Doom II, one player-controlled entity must shoot the other player-controlled entity). Collision does not imply removal, nor does removal imply collision.
Removal can also occur simply based on the decision of an agent. The most common form of this is the use of an item. For example, in Diablo II, when a player-controlled agent uses a red potion, the red potion is removed from the world. The player simple chooses to use the potion; no other activity is required.
At times entities cease to exist in the game world without any other entity removing that entity. In this case, it is not entity manipulation, but a rule that determines that the entity will cease to exist. For example, a power up may appear in the game world for a certain amount of time. When that time is up, the power up disappears and can no longer be collected. This is not a case of removal, but the power up ceases to exist based on a world rule.
In Galaga, if the player-controlled entity collides with a bullet or a non-player entity, the player-controlled entity is removed. If a non-player entity collides with a bullet shot by the player-controlled entity or collides with the player-controlled entity, the non-player entity will be removed.
Super Mario Bros.
In Super Mario Bros, when Mario uses a mushroom (by colliding with it), the mushroom is removed. When Mario collides with a coin, the coin is removed. When Mario jumps on the head of some of the non-player entities, the non-player entities are removed. If Mario otherwise collides with those non-player entities, Mario is removed.
Also, if Mario does not remove the enemy properly, i.e. lets the bombs fall through holes instead of blowing them up, or just jumps on the turtles instead of disposing of the shells, they are not removed from the world permanently and come back if Mario revisits the area where he found them first. In order to remove certain enemies permanently, a specific action must be taken.
In Sim City, when the player bulldozes a road, electric line, building, zone, or other feature of the city, that entity is removed. Tornadoes, fires, and other natural disasters also remove entities, often by lingering in the same location as the given entity for a sufficient period of time.
In Katamary Damacy and its sequel, We Heart Katamari, when the player rolls a large enough Katamari (giant sticky ball) over an item, the item is removed from the world and added to the katamari collection. Often, the item is still visible on the Katamari. This is different from collection because score is awarded by removing items from the scene. Once the item is removed it usually cannot be picked up again and remains in the katamari ball until the end of the level. However, if the player bumps the katamari, the item may be knocked loose and become avaialable for "pickup" again. The player has no real control, however, over which items are knocked loose from the Katamari.
Game Ontology Relations