Set in Seti I's Tomb

From left to right:
Heron, Set (with identifying hieroglyphs), jackal headed Duamutef, three falcon gods (likely varients of Horus, Ra-Horakhty, etc.),
the pharoah Seti I, uncertain god (but he has Thoth's ibis above him), and another jackal headed Duamutef, then likely Ra-Horakhty in the boat.
Detail of a relief at tomb of Seti I
(Enlarged and clarified from drawing of Lepsius)
(Tomb KV17 is the tomb of Pharaoh Seti I of the Nineteenth Dynasty)

We are so fortunate to have Lepsius' drawings, for some damage has occurred since the mid 19th century, when he made those drawings:

Photo courtesy William Petty

In the boat is Horus the Elder, Set, Nephthys, and Isis, another Set appears between two falcon gods, then Anubis...

In this crop of a photo by "KairoInfo4u", we can see the four deities in the boat, with their naming hieroglyphs above.

I spied him in the upper corner of this photo, and rotated him around, and yes, his name shows, also.
Photo courtesy William Petty

This is from the same photo from which the detail above this one has been cropped.
It is on the wall below the astronomical ceiling, and so far I haven't found a clarifying sketch by Lepsius.
There is, however a similar scene at Amenhotep III's tomb

Drawing from Valley of the Kings, Grave 17, credit: Lepsius
(Tomb KV17 is the tomb of Pharaoh Seti I of the Nineteenth Dynasty.)

What is Taweret resting on?

"In the stars of the Great Bear the Egyptians saw an adze or a fore-leg..." _Seth, God of Confusion_, pages 86-87
They called it 'Constellation of the Thigh'

Photo courtesy William Petty

Set does not show in his usual form in the above astronomical scene, because he is represented with other symbology.

From the museum info cards regarding a piece at the Brooklyn museum
"The strange vignette of a pregnant hippopotamus with a lion's mane, similar to the goddess Taweret, with a crocodile on her back and another nipping her paw is often found in Egyptian astronomical texts in connection with the northern constellations...."

Wilkinson explains that Taweret was also "called the concubine of Set" in his _Complete Gods and Goddesses of Ancient Egypt_, page 185. I think there is also significance to the crocodile riding her back. As Wilkinson explains in his _Reading Egyptian Art_, the crocodile is associated with Set, with lust and possibly a sort of 'will to power'. (It could likely be Set riding her!)

Of course, they changed the mythology somewhat as the view of Set dimmed.

Also, Set is in the heavens as the 'constellation of the Thigh', as TeVelde explains:
"The constellation of the Great Bear is the sign of Seth, as Orion is the star of Osiris and Sirius the star of Isis. In the pap. Jumilhac it is related that Horus had cut out the fore-leg of Seth:

"And after he had cut out his fore-leg he threw it into the sky. Spirits guard it there: The Great Bear of the northern sky. The great Hippopotamus goddess keeps hold of it, so that it can no longer sail in the midst of the gods." 2)
2) Pap. Jumilhac XVII, 11-12.

"In the stars of the Great Bear the Egyptians saw an adze or a fore-leg..."
_Seth, God of Confusion_, pages 86-87

"In the course of the history of the Egyptian language, the [khepesh], which hieroglyphic writing and the use of the word in the Pyramid texts show to have been the fore-leg of a bull, came to mean not only the constellation of the Great Bear, but also "strong arm," "strength," and even "scimitar." 4) Seth uses this scimitar in the battle against demons of disease:"

Wooden fore-leg found at Met museum in a collection of small items from the mid-Eighteenth Dynasty

So what looks like a sort of cane for Taweret to rest on is Seth's constellation. As 'opener of the mouth', and strong arm of defense, it was regarded as very powerful, indeed.