Echo

The Echoes that Slugcat meets are the spiritual remnants of Rain World's previous civilized race, the Ancients, who appear to Slugcat as large black beings with golden scales and long snouts, appearing to be sitting in a fetal position. 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 Reflections, found at the highest point in Chimney Canopy, near the gate to 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 Shaded Citadel.
 * A Bell, Eighteen Amber Beads, found in Farm Arrays high above a patch of Worm Grass, near the entrance from Outskirts.
 * Two Sprouts, Twelve Brackets, found in Subterranean region as one enters from Farm Arrays, in a cave to the right.
 * Droplets upon Five Large Droplets, found high up in Sky Islands, above the yellow lizard infested tunnel near the gate to Farm Arrays.
 * Atop the Tallest Tower, found in its own titular area high up near the center of Metropolis. This is exclusive to Artificer.

Gameplay
Echoes are non-hostile and will attempt to speak with Slugcat if they have the mark of communication, teleporting them back to their previous shelter once they are finished. They will also attempt to raise Slugcat's maximum karma tier up to a maximum of 10, and the player will awaken at their new maximum karma level. If the player meets an Echo before meeting Five Pebbles, their karma will increase by two on the first Echo encounter and one every next encounter until they achieve level 10. Echoes will always be found in a specific location, but will not be there every time. The player must go to the room the Echo appears at to trigger a flash of dark blue light, and then return at least a cycle later with either their maximum karma (or for some Echoes one below the maximum) to get the Echo to appear. The presence of an Echo is very obvious, as even at a distance the area will grow darker and unique music will play. As Slugcat gets close, flecks of gold start raining down and blue light is seen slowly moving across the screen. Enemies are typically not found during this time, and most creatures other than Slugcat that get too close are pacified, falling limp to the ground. If already given the gift of communication by Five Pebbles, the player receives a brief monologue from the Echo. If not, 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, only a flash of blue light is seen, and gameplay continues as normal. If they visit the area on a following cycle with a high enough karma level (a requirement which changes depending on your current maximum karma), the conditions described above will take effect and the player eventually meets the Echo. This is not the case for Six Grains of Gravel, Mountains Abound or Two Sprouts, Twelve Brackets, who are both found on their first visit regardless of karma level. When playing as, it is not necessary to visit the location of an Echo to make it active, as it will be present as long as the player has the required karma. Visiting an Echo location with insufficient karma as Hunter for the first time will instead trigger the same blue flash of light as seen in the other difficulties.

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 recieved 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!

Atop the Tallest Tower's Echo
You are stuck in a cycle of wrath and destruction, simple being. Gripped by raw emotions whose chains bind you, destined to this land. Shortcomings of the past haunt one and all like whispering phantoms. Listen. Let this be a warning to you... An unrewarding battle awaits, culminating in a path of no return. A perpetuity of struggles begetting more of the same. Find a way out, if you still can.

Their monologue changes if Artificer has defeated the Scavenger King

You, who have encountered a consequence much like my own. Gripped by raw emotions whose chains bind you, destined to this land. Shortcomings of the past haunt one and all like whispering phantoms. An unrewarding battle awaits, culminating in a path of no return. A perpetuity of struggles begetting more of the same. We are a pair who have forfeited everything.

Trivia

 * It is possible to complete the game without going to Five Pebbles by talking to four of the Echoes, the first raising your maximum karma by 2, and all subsequent echoes raising it by 1. Reaching the maximum karma level this way earns the Pilgrimage achievement.
 * An Echo is the result of a being with many vices attempting to transcend the cycle of reincarnation using Void Fluid, and becoming stuck between this world and the next. Looks to the 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.
 * Scavengers are not pacified by Echoes.
 * Rain World Downpour added a new Passage called "the Pilgrim" which is gained by visiting echoes. Interestingly, you must visit 6 echoes for this passage, making it more difficult to get than the similarly named and earned "Pilgrimage" achievement.