All that is known of Ymir is that he was born from the fires of Muspelheim and the ice of Niflheim when they collided in a “great bang” in Ginnungagap. In this way, he can be seen as the anthropomorphize iteration of the chaotic but endless creative potential of the Ginnungagap. He took nourishment by nursing the primeval cow Auðumbla, who also came out of Ginnungagap. He also reproduced asexually, and as such became the ancestor of all the giants and many of the Æsir as well. Due to his asexual reproduction, many consider him to be hermaphroditic. His descendants in the form of Odin, Vili, and Ve slaughtered Ymir and from his remains (the pure, primordial stuff of creation) fashioned the world. His has at least three other possible names, Brimir, Blain, and Aurgelmir. Though he is described as being “evil,” there is no textual evidence for this and the concept may be of Christian influence, as there’s little to no evidence that the pagan worldview of the Norse really had a place for the binary construct of “good” and “evil,” though “chaos” and “order” may be more likely, amoral counterparts.

Due to the nature of Ymir’s state in the mythology, this ritual will be much more about honoring the memory of a great and beloved ancestor, one who gave rise to all life on Earth (for without the pure, primal, creative force of his body, life could not have thrived). Nonetheless, bring an offering of milk to this ritual—if possible, the freshest and locally sourced milk you can find, but it’s okay if you need to stick to the basics. This ritual should be conducted outside with direct contact with the earth.
Pour your offering into a favored mug and set the mug directly on the earth. If your practice involves circle casting, cast your circle. I like to call on Jord for Earth, Ran and Aegir for Water, Surt for Fire, and Hræsvelgr for Wind/Air, and in addition I typically call on Angrboda (my patron, whom I view as a goddess of witches and völvar) to oversee my working. When you have centered yourself and are prepared:
“Hail Ymir/ Brimir/ Blain/ Aurgelmir
Hail Ymir, Mountain’s Bones
Hail Ymir, Earth’s Flesh
Hail Ymir, Sea’s Blood
Hail Ymir, Tree’s Locks
Hail Ymir, Skull Dome of the Sky
Hail Ymir, Ginnungagap’s Mirror
Hail Ymir, Element of Creation
Hail Ymir, Progenitor of Jötnar
Hail Ymir, First Ancestor…
”From you we have all come, to you we will all return. I honor you and all your names, Aurgelmir, Blain, Brimir. You, First Ancestor of Earth and all her progeny; first ancestor of all jötnar and of Æsir; you whose primal creative force enabled us to be—I offer you my greatest gratitude, honor, and love.”

Lift the mug or cup of milk toward the sky, head bowed.
“Though I can give you nothing which does not already originate with you, I bring you this offering in loving spirit and gratitude for your unwilling and unknowing sacrifice at the hands of your grandchildren.
“Hail Ymir, Whose Bones are the Mountains!
Hail Ymir, Whose Flesh is the Earth!
Hail Ymir, First of Ancestors!”
Lower the milk, and pour it out directly onto the earth. If you are near a body of water, feel free to pour the milk out into this as well. If you are unable to conduct this ritual outside, I recommend simply pouring the milk onto the ground after the ritual when you are able to go outside, or otherwise leaving it on an altar for a day or so.
“And so I honor your spirit and your sacrifice today, Ymir, First of All Ancestors. I thank you, I honor you, and I bless your name.”

Set aside the mug and bow to the earth, laying your forehead directly against the soil with your arms stretched forward and palms face-down on the soil. If you’ve raised any energy during this working, ground it out into the earth as a final offering. Again, if you’re unable to do this outside, that’s okay — you can do this indoors as well, and just focus on sending that excess energy down to the earth below your home.
Sit up and thank Ymir for receiving your offering and being with you on this day, and bid farewell to his spirit. If you have cast a circle, begin to take it up now, or do anything else appropriate to your practice to close out the ritual.