Goblin Queen (She/Her/Hers)
Yeah, Rotten Fate is definitely magical by the Sage Advice guidelines, which is why I didn’t include it in the list of his abilities that are not magical by those guidelines (which to reiterate are Flight of the Damned, Vile Teleport, Dread Counterspell, and Fell Rebuke).Well, Rotten Fate is definitely ruled out, because its description mentions what happens to a creature "killed by this magic" - so it's explicitly defined as magical.
It’s certainly possible that this is intended. Maybe Vecna has some innate means of conjuring flying spectral entities, teleporting, and negating spells that are not magical. That seems weird to me, but not out of the question. Dread Counterspell and Fell Rebuke both mention uttering some sort of word of power, so maybe that’s the angle they’re going with - the words themselves are naturally empowered rather than magically manipulating the weave. That explaination would be easier to swallow if the various Power Words weren’t spells though.