Echo

The echoes that Slugcat meets are the spiritual remnants of Rain World's previous civilized race, the Ancients. They are forever stuck between this world and transcendence. Six echoes can be met throughout Slugcat's journey. Their names and locations are as follows:
 * Nineteen Spades, Endless Reflection, found at the highest point in the Chimney Canopy, near the gate to the Sky Islands.
 * Six Grains Of Gravel, Mountains Abound, found atop The Wall region of The Exterior shortly after the player exits from the chamber of Five Pebbles.
 * Four Needles Under Plentiful Leaves, found in a grotto underneath the eastern entrance to the Shaded Citadel.
 * A Bell, Eighteen Amber Beads, found in the Farm Arrays high above a patch of Worm Grass, near the entrance from the Outskirts.
 * Two Sprouts, Twelve Brackets, found in the Subterranean region as one enters from the Farm Arrays, in a cave to the right.
 * Droplets Upon Five Large Droplets, found high up in the Sky Islands, above the orange lizard infested tunnel near the gate to the Farm Arrays.

Gameplay
Echoes are non-hostile and, upon finding one, it will attempt to speak with the player and then teleport Slugcat back to his previous shelter. This also takes Slugcat to their current highest karma tier after raising their maximum karma slightly. Echoes have set spawn-points, but are not always there. If one is near, you can tell by the environmental changes. First, the area will grow darker and unique audio will play. As you get closer, golden flecks will start raining down and everything will take on a distorted, blue-tinted appearance. Enemies will typically not be found during this time, and if one does appear it will fall limp to the ground. If the player has already been given the gift of communication by Five Pebbles, the Ancients will give a brief monologue to the player, otherwise the player will be teleported back to the shelter almost immediately upon finding them.

Encountering an Echo
In order to encounter most of the Echoes, the player must visit the area where they reside twice. The first time, when the player gets near, they will see a blue flash of light, and nothing more. If they visit the area on a following cycle with a high enough karma level, they will find the pacifying blue effect described above and eventually meet the Ancient. This is not the case for Six Grains of Gravel, Mountains Abound or Two Sprouts, Twelve Brackets, who can both be found on their first visit.

Nineteen Spades Endless Reflections
Behold this empty husk of a land...

Populated only by storms, ruins and abominations. It wasn't always thus.

I was once the Count of 2 living blocks, esteemed by my peers. I had progeny!

From within my vessel of flesh, I would perch upon this spot to observe the rising of the sun.

Corporeal matters seem so distant now. Most have forgotten this place, but I remain.

Perhaps I reminisce because I cannot go. Perhaps I cannot go because memory traps me here.

Six Grains Of Gravel, Mountains Abound
We can feel your presence, little creature.

Your attunement has become... much closer to ours.

The mark you received is an unimaginable gift.

The struggle, the cycles...

It can all fade, like a morning mist beneath the glory of the sun.

We found a way.

Four Needles under Plentiful Leaves
You have no name.

I once had! I was embalmed, adorned, readied for the journey.

So proud. There was jubilation! My name was sung, loud and clear.

Did they know? That I didn't quite leave, didn't quite stay?

Should I be ashamed? That I linger here, where my memories are kept?

Should I be ashamed that I now envy your flesh prison?

A Bell, Eighteen Amber Beads
Strange...

Something still draws me here. Even after all this time.

The weather is so different now, but the fields...

I do not need eyes to know that the grasses still sway gently in the winds.

To have grasped at the boundless infinites of the cosmic void...

Yet here I am contemplating these same fields as I once did, talking to some sort of rodent.

Two Sprouts, Twelve Brackets
A little beast!

But not as dim as the rest, perhaps?

So down into the depths you go as many others before you, drawn to the void again and again, an endless drip drip drip.

Much like these tunnels and caves that amuse me so. The bones of forgotten civilizations, heaped like so many sticks.

Did they dig too deep, or not deep enough?

Fools. We were right to drill straight through them!

Droplets Upon Five Large Droplets
Do you hear it, little one?

The buzzing in the air?

The endless chatter of a thousand thousand voices, long dead?

They are gone, and yet they speak. Neither here nor there.

Does that seem familiar? Yes, it is quite amusing for a being in my predicament!

Trivia

 * It is possible to complete the game without going to Five Pebbles by talking to four of the Echoes, each raising your maximum karma slightly. Reaching the maximum karma level this way earns the Pilgrimage achievement.
 * Echoes are the result of a being with many vices attempting to break the cycle of reincarnation using void fluid, and becoming stuck between this world and the next. Moon notes that this is especially the case for those who are too arrogant or egotistical.
 * Scavengers or some other sentient beings seem to have been aware of the Echoes at some point, as a "ghost" symbol appears near many of the Echo locations.