Hades Alone is an excellent DPS with unique abilities in the game. Although his use has declined somewhat, Alone, possessed by the soul of Hades, is a great single damage dealer. He can wipe out an opposing character with a single attack. But above all, he has two unique abilities in the game: he can swap lives with an opponent (or ally) and he can link two characters (a bit like Hades but better).
These two abilities are very powerful and can turn a game around at any moment. So why has his usage declined? Because our friend Alone is very susceptible to control, he has no mechanics to counter this. Furthermore, it's a meta with many studies and defenses, which has greatly reduced the damage he can do. Still, with the right bans (Camus Surplice above all), he can win a game on his own.