From Worms Knowledge Base
Activating this weapon causes the entire game to revert to a former state. A player selects the weapon and activates it with one of his worms during his turn, and the round will then continue from an earlier point in its history. Land that has been destroyed will be returned to its former condition; weapons that have been used will be available once more in player's inventories; worm, mine and barrel positions will be restored. Worms that died will be revived, health will be restored and round time increased.
The game returns to the state that it was at the beginning of the last turn of the player that activates the History Eraser, allowing the last minute or two of the game to be re-written, depending on how long and how many previous turns were.
The player who activated the weapon will then be able to carry out his turn again, as he did before, but will have the opportunity to do something differently.
Time travel is of course impossible. But the illusion of time travel can be manifested by saving details of a game at a particular point in time and then reloading those details when the game is told to by the History Eraser weapon. And saving details of the game at the end of every turn shouldn't be that hard.
The game would need to keep simple details on the location, name, team and health of each worm, barrel, mine, crate and piece of fire. It would then jot down the weapons inventory of each team, the round time, and whether sudden death was activated or not (which could be derived from round time). Details on land deformation would be a bit trickier, it would take far too long for the game to save all the information, including colour information, in the map itself. Instead, it could save space by saving details on where land has been lost, and then compare this with the original undeformed map to recreate the deformed map. Added terrain, such as girders and arrows, have a set number of shapes and colours and so the game would only need to store information on the type of object placed, where and how it was placed, and whether it has been partly destroyed or not.
This information could constantly be over-written each turn.
When the History Eraser is used, the information would be extracted to recreate the entire game as it was when it was saved. The whole process would be just like reloading a Saved Game. Clearly, there are a couple of limits involved in using this weapon. It would not be able to be used at the beginning of the game, as there would have been no previous state for it to return to. A simple, unremovable Delay of one turn would solve this.
For avoiding a never-ending game, a team would have to wait N turns before using another History Eraser, being N = U + V + 1 where U is the number of times the team used the History Eraser and V the total number of times all teams in the game used the History Eraser. Also, returning to a previous point in time would not restore the weapon that caused the jump back in time, lest the universe collapse in on itself. Lastly, turn time would not be modified, so this weapon would not give the advantage of extra turn time.
The History Eraser would prove to be an invaluable tool, a super weapon of undefined proportions. It could be used to give a player another chance at that tricky manoeuvre, to undo a mistake, to undo another player's deadly strike or to make use of an opportunity you previously missed.
The strategic potentials in this weapon are as many as there are strategies in the game entirely. Undoing a turn is as much a strategy as performing the turn itself.
If at first you don't succeed... try again, for the first time. Aside from sparking the inevitable witty and confusing chat dialogs about the logic of time travel, this weapon could be ample opportunity for some fancy time-travelly special effects. And the concept of time travel is perfect for Worms.
The maniacal laugh from the Scales of Justice would make a good sound effect.