Shadow Saiyan is a transformation that is triggered the same way Super Saiyan is triggered with the exception that only a Saiyan blessed by a god-like being can reach. Because of the raw dark or light power being transferred to the Saiyan through the blessing, the Saiyan has to be unsure of whether they are good or evil or else their body try to amplify it too much and burn out its body or will be driven insane by grief and try to destroy the multiverse.