This spell might be complicated to pull off or maybe even plain out impossible, but I think it's a cool idea none the less, so here goes..
This is a End Game Spell, Very High Level, Very Ultra Rare, but it has a very interesting feature behind it. Before I get into what the spell does, I need to side-track to compare this to something else.
System Restore Points...and/or Auto Saves. Think about when you create a "Restore Point" for Windows or when the game Elemental makes a "Auto Save". For this spell to work the game will have to make "hidden auto saves" and store them in memory, say every 25 to 50 turns or so. Now for the Time Travel spell description...
When you cast the spell "Time Travel" it brings up a pop-up menu that asks "To Which point in History would you like to Travel?". Then it will show you a list of the hidden "Auto Saves" that it made but it won't list them by turn number. Instead it will list them by whatever the most recent event at the time the save was made that happened in game was. The player then chooses which point in the game's past to travel too even as far back as Turn 1. The Spell MUST NOT go back to anytime that would be considered "Recent". In fact, I don't think this spell should even be Allowed in Any Game that was less then 500 turns old. This way the spell has Serious Ramifications when used and isn't just the same as re-loading the game and only loosing 25 turns or so. The Spell MUST go back a 100 turns or more. This spell will only be useful in Large, Epic Games, that take days or even weeks to complete. The Spell will then reload the game at that "save point" or "auto save" but it will the load your Sovereign with his Stats, Skills, Learned Spells, and Personal Items that the Sovereign had when he/she cast the spell "Time Travel". Perhaps also make it possible for the Sovereign to take one or two units with him (maybe even a dragon if he has one).
Why Is This Spell Useful for Game Mechanics? :
Imagine that it's near the end game and you realize you're going to loose after spending 10 or 20 hours on the same Huge Map (or even Medium Map). Maybe you left a powerful enemy alone for too long and now they are about to win the game with the "Spell of Mastery" or they are about to roll over your last city with their "Stack-o-Doom". Either way, it's painfully obvious that you're Not going to win. Rather then restart the game or re-load the game lets give the player another option. By casting "Time Travel" you can travel back to a much earlier part of the game with a Powerful Sovereign (and maybe a unit or two). You can alter History its-self by going straight after the enemy that you now know will get super powerful if you let him.
The spell "Time Travel" has Serious in-game ramifications how-ever. It doesn't let the player go back only by 10 or 20 or 30 turns. It goes back Hundreds of Turns meaning the player now has a LOT of work to do Over Again. Still, it's better then losing or having to start over and it gives the player the advantages of having a Powerful Sovereign to do everything over again with plus the knowledge of where resources are located on the map as long as the player can remember (FOW will be back).
Another issue this spell addresses is the fact that we all know players (and have been guilty of it ourselves) who like to Re-Load the Game every time something doesn't go their way. Perhaps they loose their favorite champion or loose one of their main cities or just realize they aren't going to win this game and decide to start over. With the option to Time Travel they might not simply re-load the game or start over. It gives the player a incentive not to "cheat" by re-loading and instead gives them the chance to go back and fix mistakes they made.
As a Reward for finding the spell or using the spell the player gets the advantage of being Very Powerful when all his enemies are much weaker, which is why I think the spell should be Very Rare to be "fun". It's almost as close as a "I Win" type spell as the "Spell of Mastery" is. Casting the Spell of Mastery is the Magical Tech Tree way of winning the game so the player is about to Win Anyway. This way the player can have even More Fun on that same map/same game by going back in time to really humiliate their enemies by stomping on them being leveled up. To add even more Fun imagine if the player is allowed to time travel and take that Dragon they just recruited with them. Sure, the player would face the "possibly" boring idea of having to play the exact same map with the exact same enemies again, but this time the player would be able to have fun owning them with End Game level spells and maybe a couple Powerful End Game units. As I said it's almost as much of a "I Win" spell as the "Spell of Mastery". In a way it's just an excuse to have fun on a map you were Already About To Win Anyway....or Lose Anyway.
This spell needs to be Super Rare and not appear on anything but Medium Maps or Larger. Perhaps it should even be considered a "Epic" spell or come from one of those items you'd only see once every 400 games or so like "Frogboy's Diamond Golem Quest" idea. This spell is also for Single Player Games Only as it would be very unfair and un-fun for Multi-Player. Seeing as how this spell could save a player from losing the game just as casting the Spell of Mastery would before you were about to be conquered militarily, this should Definitely be Very Expensive to Cast using Most of or All the casters resources. Also when the player Travels back through time, if they take any units with them then in the Time the player travels too he/she must be able to have the incoming resources to pay what-ever upkeep those units have. This means that if the player travels back in time and takes a Dragon with them, and that Dragon eats 100 peasants a day, then in the time the player traveled too they need to have enough cities to be able to provide those 100 peasants a day or the Dragon would leave.
I can also think of another version of Time Travel that doesn't work anything like the above version. The Second Version would still be Super Rare and Expensive but instead it would only allow the player to go back in time by One Turn and ONLY Once, Period, and then the spell could never be cast again during that particular game. I think I'd rather see the above version implemented if either of them are considered though.
Thoughts or feedback?