I'm gonna take another look through the volunteers already suggested, but for my part...

I'm volunteering both Blaze and Ghost (this account) - but separately, because acting as emotional ballast for each other is what they do and that is just not sporting. Both of them have plenty of nightmare fuel to offer if anyone wants to get chased around pustulent lunar caverns by ravenous alien mummies.

Blaze's personal nightmares include: being attacked by (and killing) everyone she's ever met, a confusing jumble of fragmented memories from the losing end of a world-ending war... and her own mental instabilities causing her system to reboot and wipe her memory. Ghost's worst nightmares are losing his Guardian and being hunted through the wilds by dark creatures (again).

Also going to throw in Stratos/auspex_caelo, who has some great potential nightmares about brutal invasions of his homeland and/or being ordered to hand civilians over for torture... or worse, having no way out of doing the job himself. If soul-blighting cruelty and moral compromises sound more your creepy style, lemme know!