With the addition of the endless mode, I’ve been thinking about a cyclical old one. With standard old ones the goal seems to be to gain as much power as you possibly can in a single attempt, and if you really need to go back to sleep or you get sealed then you take another chance later.
My idea is an old one that is only able to gain a small amount of power within any individual cycle and could only stay awake for a limited time (which increases with every cycle) without causing yourself harm. Over multiple cycles you would slowly get stronger, and once you free yourself from the seal you would be permanently awakened.
One power tree would be unless within any single cycle, but would give you powers that would be useful over longer time periods.
For example:
1) A power that corrupts the seed/womb of (captured?) individuals. It would be useless in the current cycle, but it would allow you to corrupt their descendants much easier when you run into them in a later cycle. Or it could be something more interesting, making their descendants passively weaker/more cowardly, or simply make them more and more monstrous with each passing generation. Or make them turn all into monsters (with a strength based upon how many generations its been) when you activate a trigger.
2) Freeze some agents/corrupted heroes/captured individuals in hibernation until you awaken and unfreeze them. Your agents would be able to rejoin you at their current power (allowing you to keep some strong agents for another cycle), while kings that waken later could cause chaos in the nation they used to rule (but don’t anymore due to being “dead” for hundreds of years. You can freeze as many agents as you want, but there is a significant cooldown between each use, which means that to freeze many agents you would have to take the first of them out of action long before you go back to sleep.
3) Curse a nation, making their actions worse on average. This would take a long time to take effect, and while you are awake it would be unobtrusive and minor, but over the centuries the game runs in endless mode it could have a pretty huge effect, and could even result in the eventual destruction of the nation (via civil war or conquest) where it would have otherwise have thrived. You can only curse one nation at once.
4) Whisper into the mind of immortals as you sleeps, corrupting them over the centuries. Obviously wouldn’t work with rival old ones or Those That Remain, but dragons (if they are in), elves, and monstrous immortals would be significant targets. The ability must be targeted before you go to back to sleep.
5+)
The other power tree would give you shorter term powers which you would use while you are awake. I’m not quite sure what this tree would consist of, although my current thoughts of it mainly consist of it largely revolving around sleep. For example:
1) Puts a target into an enchanted sleep for 5-10 turns after a few turn delay.
2) Prevents the target from sleeping. When used on heroes it slowly driving them insane (but doesn't corrupt them). When used on agents it increases their efficiency, increasing the speed at which they complete rituals and travel by 10-20%.
3) Temporarily awaken the sleeping elemental forces in an area, creating an earthquake/tornado/volcanic eruption/flood depending on the primary elemental force nearby.
4+)