Horns and Missing Eyes: Spoiler !!!
Notice the large horn is where the Rinnegan is missing.
Notice the spike is where the Rinnegan is missing
But Kayuga had two horns and the Shinju's power
But later, if she is indeed the reaper,
Well, she has no eyes. Which means she has no Rinnegan. Which means she has two horns instead.
Even if Kayuga isn't the reaper, the fact that the Reaper is directly related to Hagaromo's Tablet tells us it's powers are connected to Sage/Juubi/Rinnegan etc.
The Kin Gin brothers are related to Hagaromo, but they seem to have very dark eyes. Almost too dark. They have little or no irises.
They have very large horns
Perhaps when one possess the power of the Juubi, where they do not have the Rinnegan, they have horns instead. (notice the 6 flames around the reaper, 6 paths perhaps?)
Obito had a very small horn on is Rinnegan side while Madara had no horn on the Rinnegan side.
What accounts for this difference? The Rinnegan Obito was using wasn't really his, he barely was even able to tap into its powers. Therefore only a partial horn manifested.
I don't know what all this means. But I'll get to the bottom of it.