Flashback event guide

A few people have asked about guides for the flashback event : when you can complete challenges etc.

It's really pretty straightforward as there are seven that can be completed equally easily at any time:

Full Clear: The Fetid Pool: Fully clear the Fetid Pool.
Identify a Unique Item: Identify any Unique Item. You can trade it away afterwards.
Kole the Cruel: Kill Kole in Cruel difficulty or higher.
Room to Grow: Create a medium-sized Hideout.
The Golden Hand: Complete the quest "Through Sacred Ground" in Merciless difficulty.
Full Clear: Vaal Fragment: Fully clear a Vaal Side Area that was created using a Map Device.
Kill a Unique Map Boss: Kill the boss of a Unique Map.
Reach level 85: Reach level 85.

The remainder of the challenges are one per old league that is being flashbacked. Some of them you have a chance to complete at any time, but there are just some times when you are more likely to do them (e.g. you have a chance of finding a tormented spirit, and therefore chasing it into a unique, at any time, but your chances are much better when the torment mod is on because you get additional guaranteed spirits).

I have made a colour coded table to help you see easily which of these challenge you can complete when: RED means you cannot do the challenge except by using Zana crafts on maps;
YELLOW means you might complete the challenge through normal play but it is not your best chance to do it;
GREEN means the relevant mod is active and you have the best shot at completing the challenge.