Ker
Ker is a Rank S Elite Mark found in Endwalker. Ker is one of what the player base calls SS Ranks
Killing the Elite Mark will reward the player up to 
400 Sacks of Nuts, 
200 Allagan Tomestones of Poetics, 
50 Allagan Tomestones of Aesthetics, 1 
Cracked Anthocluster and 1 
Cracked Dendrocluster.
Coordinates
| Zone | Coordinates | Level range |
|---|---|---|
| Labyrinthos | (X:25, Y:16) | 90 |
| Thavnair | (X:24.3, Y:16.8) | 90 |
| Garlemald | (X:19.7, Y:23.8) | 90 |
| Mare Lamentorum | (X:18.7, Y:30.4) | 90 |
| Elpis | (X:22.7, Y:19.8) | 90 |
| Ultima Thule | (X:15, Y:29) | 90 |
Spawn Conditions
Trigger
Each time a Rank S dies in Endwalker areas, it has a chance to spawn four Ker Shroud throughout the zone. Once four of them are killed, Ker will spawn.
If they spawn, the game will announce: "The minions of an extraordinarily powerful mark are on the hunt for prey."
They will withdraw exactly 5 minutes after this message if not engaged, or if disengaged by dying.
When all of them are killed, Ker will spawn.
Time
Ker has no respawn timer. It is randomly decided by the server upon each Endwalker Rank S death whether it will spawn minions or not. Because of this, if the spawning fails because a minion withdraws it has no effect on any timers. It could theoretically spawn minions after every single Rank S death in Endwalker in a row if the game decided to randomly do that.
Tips and Tricks
When it spawns, the game will announce "You sense the presence of a powerful mark..."
- Heliovoid is an untelegraphed circle AoE slightly larger than the hitbox applying a
Vulnerability Up. Move away from the target ring. - Ancient Blizzard III is an untelegraphed donut AoE applying a Vulnerability Up. Move inside the target ring.
- Minax Glare applies Temporary Misdirection to the closest 32 targets, making their every movement in a random direction. Keep trying until you run out of the next mechanic.
- Whispered Incantation applies a buff of the same name to Ker which remembers the next spell.
- Eternal Damnation is a Gaze.
- Wicked Swipe leaps to a target and casts a small, telegraphed conal AoE. This attack is very far into the rotation.
- Ancient Holy is a proximity AoE. Move away.
- Ancient Flare applies
Pyretic to the closest 32 targets, causing damage to be taken every time they attack. Sheathe near the end of the cast until it expires. - Fore Interment is a large conal AoE in front applying
Doom to those hit. - Rear Interment is a large conal AoE behind applying Doom to those hit.
- Right Interment is a large conal AoE to the right applying Doom to those hit.
- Left Interment is a large conal AoE to the left applying Doom to those hit.
- Whispers Manifest casts the remembered spell.
- Mirrored Incantation grants stacks of Mirrored Incantation, which causes the next interment casts to be inverted and happen in the opposite direction of what they say.
Watch these stacks because once they run out, the interment casts will happen in the direction they say.
Description
“Myths serve myriad purposes, but one of the more prominent sorts is cautionary tales. Among such stories, those of Ker may be the most terrifying.
It is said that Ker appears on the battlefield to feast upon the souls of the dead, hunting down the living she lays eyes upon unto the ends of the earth. She brings naught but a swift demise to those who dream of glory.
If I was to postulate that Ker is not merely mythological—which I do—she must be some manner of ashkin. "Undead," in layman's terms. This would explain how millennia can pass without a sighting...
However, legend has it that her "shrouds" are ever in search of new prey for their mistress, so hope yet remains. Should you glimpse these spirits in reddened rags as you sheathe your own bloodied weapon, pray keep your wits about you...— Basildere, Old Sharlayan Aetheryte Plaza, Old Sharlayan
Lore
“One of the more prominent sorts of myth is the cautionary tale, meant to terrify the listener into prudence. For instance, it is said that Ker appears on the battlefield to feast upon the souls of the dead, hunting down the living she lays eyes upon the ends of the earth—that naught but a swift demise awaits those who dream of glory. Basildere postulates, however, that this warning is not merely mythological: Ker may instead be an ashkin that could re-emerge at any moment, heedless of the intervening millennia. Those who wish to err on the side of caution in the face of this disturbing possibility are advised to keep one eye open for spirits in reddened rags appearing at battle's end, for these are Ker's shrouds, in search of new prey for their mistress.
— Encyclopædia Eorzea Volume III, p. 302