Not well defined at all. But Void seems to be able to bend space.
Slan doesnt seem to have shown any unique poers other than sadomasochism. When she struck Gatts, it was an unnatural unholy wound, but probably all the god hand could do that, as well as manifest in certain objects.
Ubik can conjure illusions based on ones inner desires.
Conrad appears to be a pestilence bearer, considering what he did with the rats and how he used them to assume a form briefly.