For my villain and sidekick I'm going to have them share the same body. This means that the sidekick becomes loyal to the Elder God because he has an interest in his body, and wants it back. So the Elder God has possessed the sidekick to escape from his banishment and now like a parasite feeds off of the sidekicks strength to make himself stronger. In effect this makes the sidekick weak and gaunt where he once was a strong man.
When I design this character I need to design what the sidekick looks like when he's in control, and then what the Elder God looks like when he is in control. I also need to come up with an explanation of why the sidekick sometimes gains control over his body when the Elder God is so powerful, as well as an explanation of how the Elder God gain access to the sidekicks body.
The hero is the sidekicks brother so he has an invested interest in defeating the Elder God and getting his brother back. Both brothers are Native American.
It was also suggested that I try and connect the native american mythology of gods to the Elder Gods HP Lovecraft describes as it needs to be obvious that this is an Elder God and not just any god. Looking at a book that Meg lent me I scanned in a few of the images of Cthulhu and some of the text that I though was relevant. The first image at the bottom actually says that most of the worshippers were west Indian.
In these images Cthulhu is shown as being massive and very tentacled. While trapped in the sidekicks body when he comes out hes still going to be large and imposing but he will be a lot smaller confined to a body that can not contain his whole form. I'm going to do a bit of research and try and address the problems in my characters story and start to write my logline and character profiles.