One underrated, definitely solo-viable character is
His match-up spread (at least from observing high level players and my own observations) is that of a top tier. The only genuinely agreed -1 mus for sonic are
and
, with Wrath making a solid case that
and
can also be unfavorable matchups. But with that said, Sonic arguably doesn't have a single -2 matchup in the game, and actually does pretty well against most of the other top tiers, either going even or straight up having +1s with
(which even Leo believes Sonic wins) and
. Sonic has a lot of versatility with his moveset in this game mainly due to him actually having utility on everything in this game (unlike Smash 4 where his moveset largely sucked outside of his brokenly-good side b, uair, bair, and spring), and as a result he isn't really counter-pick-able. The issue with Sonic, and why he's rightfully seen as a low-high tier, is just due to the character's own issues, like his dysfunctional uair and spincharge, and his kill power can be really bad at high level. IMO if not for sonic's neutral being so challenging as well as his own inconsistencies, he'd easily be one of the best characters in the game.
He goes even or wins against almost the entirety of the cast, it's just up to the player to actually have the patience and ability to outplay the opponent at higher level that holds him back.