Any (new) play mechanics or variations on current ones that you'd like to see tried, 2D or 3D?

I like this idea, it would not change the gameplay too much and still make bouncing onto badniks more rewarding; skilled players can use it for acrobatic tricks and would be nice to watch in a speedrun or something.
And BTW Nago in Kirby's Dream Land 3 is already kinda like this... he has 3 jumps, if you stomp an enemy while holding the jump button, the count will reset and you have 3 additional jumps even if you didn't land.

I like those ideas as well. The fork does not need to be tied with time, it might also be due to different events and actions performed by the player. Let's say that you play Flying Battery: if you find the engine room and manage to destroy it, you enter a different branch of the story where the ship crashlands into a different zone, while if you reach the top deck you fight Eggman on there and the ship is not destroyed, bringing you to a different place.

Regarding fail states, I agree as well. Super Mario Land 2 had that thing that when you did a gameover you would lose a golden coin and need to defeat the boss of that coin once again. I thought it was very interesting as a concept, because even if the game was finished, the fact that you could still lose a coin and regress in the story, unlocking more stuff to do, was almost like if the game refreshed itself. Too bad that it's so easy to grind 99 lives and forget that gameovers even exist in that game... also it only really works if the game is fun to play. I know, every game should be fun, but sadly that's not always guaranteed. Think of Breath of the Wild... imagine if each gameover would steal 10 korok seeds from you and you had to get them back... it would definitely be not fun at all.

In the context of Sonic Frontiers where the combat system is part of the core gameplay, it would be a good idea. Asura kinda does that already, to some extent... I wish there were more enemies that you had to disassemble like that one, and also that you have to run over as if they were part of the terrain.

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Regarding my idea of A to B missions in the open zone, I was thinking... would something like Crazy Taxi but Sonic work in a sandbox? Not necessarily an entire game, just a game mode or a minigame, I don't know... Maybe a mode where you have to grab Chao/Kocos and bring them to some specific places, until the time runs out (each deliver completed will work as a checkpoint in the arcade games and increase the timer a bit). I think it would be fun especially in the endgame when there's nothing to do anymore.

 

Metroidvania Sonic on a huge, interconnected multiple zone 2D world.

 

What you're advocating for in general is a solution to the orientation problem that Sonic has never tried for reasons that I don't really understand -- one big arrow or sign telling you where to go (diegetic or not). I suppose it's a good solution, and I'd like to see how it goes. Has any fangame tried that -- as opposed to either the collectathon approach or a mostly automated A-to-B?

Because I really like racing games like that. Midtown Madness is a lot of fun.

 

Timed missions are basically Gamma's whole deal. But arrows? It was done exactly once.

 

Not that I know... even Sonic Utopia has one sinle objective at the corner of the world, making it more like a regular level with a very wide map rather than a midtown madness type approach (now that you mentioned, old school checkpoint-based games like Midtown Madness and Carmageddon fit the idea).

In official games, the closest thing was the Sonic World mode in Sonic Jam... not quite the same thing, because often the goals are hidden/not hinted and you have to search for them by yourself (no big arrow), but the approach is similar to what I have in mind, the sandbox is so small that in most cases even if the points of interest are hidden, they are easily spotted by running in random directions for a couple of seconds (at least in the earlier missions).

I forgot that Frontiers had a few of those not automated A to B timed missions too, but they were very basic; most of them were so short and with a strict timer that you could not really take the path you wanted. Some were fine though: I liked for example when it asked you to climb the tower in Chronos Island... the tower has several different alternate paths and you can choose the one you prefer, as long as you reach the top; sometimes, even if you fall from a path due to an error, there's more terrain and HA locks below, so that you can land on a different route and try again. That's kinda the 2D philosophy of multiple paths. On the other hand, the towers in Rhea Island were too much linear, and still you could take all the time you wanted, even though the sense of urgency is still present due to the story.

There's also treasure hunting in the Adventure games, but the fact that your goals are hidden and you need to collect hints or use a radar in order to get an idea of where to go, defeats the purpose of mindless running toward your goal without focusing on exploration (because even if there's a timer, exploration is still your primary way to find your goal, it's needed and breaks the linearity).

There are some more arrows across games (I think marble Garden has some), but very few games use them outside of being pure decorations, indeed. That's because usually in 2D or linear games, your direction is pretty obvious (go right, go forward, follow the only path).

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From a strictly gameplay prespective, there's one thing that I would like to try out. I'm not sure if it works well because I never tested it and it's a pretty technical detail that you can't really have an idea of until you actually experiment with it, so maybe it's even a bad idea, I don't know.

Have Sonic gain a mini-drop-dash each time he lands while holding down to roll. It would not happen if you roll from walking, it only happens when you roll during a landing. The mini-drop-dash is less powerful than the real deal, but preserves the carried momentum and adds some more (maybe until a certain cap is reached): think of the air dash in the Advance games, but on land; it can be repeated several times in a row to gain more speed. The difference compared to the regular drop-dash is that you don't need to charge it, so you can do it even after a very small jump, as long as you have enough horizontal momentum to trigger even a short roll.

When you decide to roll on a landing, it's usually because you want to keep the flow and attack/defend from eventual hazards; I think that a little bit of additional speed is never unwanted in those situations. It can be a Sonic exclusive too, for example, Tails and Knuckles might not have this ability.

It does not require additional input other than the direction down, so it doesn't overlap with other actions. If you don't want the additional speed boost, you could just land without rolling (you can always roll after landing, it does not trigger the move)... if there is an enemy ahead though you usually want that speed boost.