The blackout cycle is the core game mechanic. This is where the enemy "echoes" learn and unlearn abilities. There are 3 stages: Light, Dark and Total Blackout.

Light stage:
This is the stage where the palace learns abilities. Most of the actions you make, are remembered.
The palace learns the abilities, not the echoes. The echoes are rebuild after each blackout with new abilities "installed".
The duration of the light stage depends of what the palace learns. Some actions cause the palace to reset fast. Others - like playing instruments and and picking up stuff - doesn't cause a blackout, unless in combination with other actions. The duration also depends on if the echoes notice you doing the actions.

Dark stage:
In this stage the palace doesn't record your actions. You can run, shoot, leap etc. without the echoes picking it up for the next cycle.
Some elements like energy cells and save arches are disabled during the dark stage.
If echos are killed in the very last seconds of the black stage, they will most likely be destoyed in the next light cycle.

Blackout:
The palace resets, echoes are replaced/rebuild. The player suit locks up, unable to move.

You don't want to teach the echoes everything during a light cycle!
- Keep it down to a few things, if possible. Keep the other abilities in reserve to get out of tight situations.

Running and shooting can be very dangerous things to teach the echoes, unless you know what you are doing. If you have taught the echoes dangerous moves, it's a good idea to keep a low profile in the next light cycle.

It's not really needed to play ECHO as a stealth game if you're not into that. Just hide when danger is close and you are out of other options. If you are out of the echoes vision cone they don't notice you -
but can hear you if you run.

Remember echoes are reset after each blackout, so no need to hunt them down. Just push them away if that's enough to get you where you want to be.

The description of the save arches is found in the function boxes, and has been overlooked by some.
But they have one very important function: They save your progress when you walk through them!
The save arches also has the ability to show you all the orbs needed to unlock "caste" elevators.
They can be seen through walls and in the dark if you use your area scan. They will be shown as an outline - like the enemies - if you are close to one.

If you quit the game after having saved at a save arch, the game will pick up from that point if you choose "Continue".
If you choose "Levels" instead and start the level you are at, the game will start at the beginning of the level, forgetting your progress in the level.

If you find the game too easy, harder modes are unlocked when finishing the game: Ultra Hard and Legacy mode.
Legacy mode makes the echoes remember stuff they've learned for more light cycles.

Hard mode is available from the start, but a good way to make the game much more difficult right from the start, is to remove the HUD sphere. Then you can't detect enemies sneaking up on you!

If you pick up every orb in the levels with the large exit elevators, you get the unlocks. One for each level.

Voices and capacity bits you have picked up are saved when you finish a level or enter a save arch.
If you replay levels you don't need to finish the level to store the pickups, just enter a save arch and quit the level.

Voices and capacity bits can be heard and seen when you use the area scan. They will pop up with a ping sound and animated rings.