The defining feature of the 9M730 Burevestnik (Russian ‘Storm petrel’, NATO reporting name SSC-X-9 Skyfall) is its nuclear propulsion system. Its small onboard nuclear reactor gives it effectively an unlimited range.
Unlimited range means:
the capability to loiter in the air for days on end.
the ability to circumnavigate the entire globe, if necessary, to reach its target.
the capacity to evade concentrated defenses, and strike from unexpected attack vectors.
Stealth
Since it’s a cruise missile, the Burevestnik can hug the ground on approach at altitudes below enemy radar’s ability to detect, making interception challenging if not impossible.
That’s because no traditional ballistic flight trajectory and no range limits means there’s no point where defenses can be deployed en masse to stop it.