Yemós
Also found as Yemo. Their name means "Twin" or "Double"
Yemós is the ruler of the afterlife or Underworld (Dhubnóm). They are the deity of the dead and may be prayed to by those about to die, or on behalf of those who have just died. Yemós is also characterized as bigender.
Yemós is not the deity of death, however. They are the one who rules over the dead, but they do not make them die, or decide when they will.
Yemós is the twin of Mónus or Mánnus and both are the protagonists of the Proto Indo-European creation myth:
Proto Indo-European creation myth
From the primeval chaos (G̑hā́nos) eventually emerged the universal principle of order, the Ártus. From these two emerged a cosmic egg, the Olyōwyóm. After it hatched three beings came into existance: Ammādhēinús, the primeval cow; and the twins Yemós and Mónus. Ammadheinús then nourished the two twins.
Eventually, Mónus sacrificed Ammadheinús and his own twin Yemós. Mónus then dismembers the body of Yemós and uses the parts to create the world: Their skull becomes the sky; their body the earth; their hair the trees and grass; their blood the rivers and seas; their brain the clouds; their bones the mountains and stones, etc. From Ammadheinús' body came all animal life.
From their sacrifice, Yemós became the first to die and also the first immortal, becoming the first deity after their sacrificial death, ruler of the underworld and of the dead, of which they are the first. Mónus became the first priest, the first king and the first mortal. From Mónus all humans descend.
After their sacrifice, Yemós begot the twelve primordial deities, the G̑hṃg̑ṇ̄tṓs, from which in turn descend the Deiwṓs and from which descend the Amséwes and all the lesser deities. So Yemós is the ancestor of all deities.
Offerings
taken from here
Skull (possibly with crown or gold wire(s))
black lantern
burial shroud
tomb image with spirals (maybe made into a candle holder)
inverted cauldron
red and black woven rope hanging from ceiling
crow or raven feathers wrapped in gold wire
depictions or imagery of skulls or tombs
Dirt with flame-colored stone
a large golden bead, or a number of small golden beads
Devotional acts
Learn about and honor your ancestors/those who have passed
Keep family heirlooms
Visit the graves of family members and leave flowers
Visit cemeteries and if allowed leave flowers
Learn about death and how to address it in a healthy way
Work on learning how to let go of the past
Visit ruins or ghost towns (safely!)
Associations
Skulls
Graveyards
Darkness
Black and red
Crows and ravens (because of their black feathers)
The feast of Samhain
October
Descendants in later pantheons
Yama (Vedic)
Yima (Iranian)
Ymir (Nordic)
Remus (Roman)
Hades, in their role as ruler of the underworld (Greek)
Dis, in their role as ruler of the underworld (Roman)
Finally, here's their wikipedia article (shared with their brother)