How it works
Beehind uses the same methods as Odysseus for over-the-air downgrades, where kloader loads a decrypted image and allows you to bootstrap a pwned iBSS which initiates a restore to a custom IPSW. For other downgrades, Beehind uses iFaith's method of downgrading. According to the developer, future versions of Beehind will adopt Odysseus's methods for a more stable downgrade.
Beehind only works on some jailbroken 32-bit devices with an untether that has tfp0 enabled. The latest versions of TaiG, Pangu9, Pangu8, Pangu, evasi0n7, and evasi0n all have tfp0 activated. Also, this will *NOT* change your baseband. If you go too far up or down with iOS version, it may be that the version of iOS you restored to does not understand the baseband left behind by the prior version of iOS. If that happens, you will not get past activation and you cannot re-jailbreak the device. As a consequence, the device will remain in activation limbo and you'll have to restore to the currently signed version of iOS.