When the Doctor and Nyssa are escaping, they run into a guard who fires his weapon at them. The laser beam clearly touches Nyssa but she behaves like it didn't and runs away.
Omega was destroyed at the end of The Three Doctors: Episode Four (1973). Here he is resurrected, but absolutely no explanation is given as to how.
Hedin says that Omega was the first Time Lord, but that was actually Rassilon. Omega was in fact a stellar engineer, who's work enabled the Time Lords to access a new power source, but he supposedly died in the process.