Anything with 65% speed stat or higher. I counted it up the other day… 94/270 legendaries and mythics (roughly 35%). You can see them all listed here: KD's Legendaries/Mythics listed + stats
It deals a lot of damage and those monsters will naturally have low HP so it’s only earth monsters or ones with very high defence that can survive being one-shot. I can’t remember the exact damage numbers but I think many mythics survive, which seems fair enough!
Alphastorm is basically storm’s version of Ahuizard. I expect it to see just as much play.