I was messing around with some Sonic strats today, trying to figure out if the Spin Dash (Pretty sure that's what they call the Down-B?) is ever useful.
It has an absurd start-up time compared to the rest of Sonic's horizontal movement options, it isn't particularly fast, and it doesn't deal much damage. If you manage to connect (and your opponent fails to react at all during your massive end-lag) you can get a followup with a short-hopped Fair or something; but you could do more damage using Boost -> basically any other option and use a different followup.
I compiled a list of useful situations for the Spin Dash:
1. You want to feint an approach and use the Spin Dash's jump functionality to hop over or above the opponent instead. This would be a good use, except there's no reason your opponent should expect you to connect the spin dash in any case.
I don't ever consider using the move to be my best option for approaching, evading, dealing damage, or even just messing with spacing. It's hard to beat Boost's horizontal movement capabilities, so I think that Spin Dash should either do something else as a main focus or allow for a different sort of horizontal motion. I was considering the implications of being able to cancel Spin Dash into a taunt at any time. If one were to use a taunt during the move, one could instantly stop to taunt. Sonic has (I think) the unique property of instantly-cancellable taunts, so one could then act with liberty after immediately stopping. This is assuming that momentum wouldn't be maintained between the Spin Dash and the taunt, and I'm not actually sure if it could work that way. The move would then exchange higher startup time (compared to Boost) for more options at the end of the move.
For example, if I want to move across the stage and use Up-Smash, I have a couple options.
1. Walk over and use the move (lame, but accurate.)
2. Run over while timing the hyphen smash (really fast, but inaccurate)
3. Boost over, pivot/crouch brake and then use the move (can be very fast, but easy to evade)
Or, with this change:
4. Spin dash to the side, taunt, up smash (startup animation gives it away immediately, but very fast and accurate)
The alternative would be to give a reason for a player to actually connect the move. (So that feinting could be useful.) Somewhat more damage, or popping up the target to a better combo angle.
Just spitballing. If anyone else finds the move to be useful, I'd love to know how.