Except for Sonic the Hedgehog Genesis, which is a port of Sonic 1 (albeit one the fanbase doesn't particularly like).

Momentum can be used to make the game fast placed; take a loot at Sonic games for example. Or you could look at Celeste, particularly speedruns of said games. (In Celeste, it actually takes a bit of getting used to the way momentum from jumping off a platform works; a good portion of my Chapter 1 deaths were getting used to this mechanic.)

Momentum on slopes is good. It's not so good for precise jump especially where the edge of the jump is not very clear.

That's effectively what i said. IMO, sonic's a terrible example, though, since inertia seems to only apply to stopped sonic from my experience, with the exception of the speed shoes powerup. The kicker is, sonic manages to be slower than mario (Thanks matt patt).

The Mario games *do* have momentum, and to reach speeds comparable with the speeds Sonic can reach, Mario needs to take advantage of this (like sliding down a slope, then jumping while not holding left or right to conserve that momentum).

Right, but if you look at the context we were specifically talking about the Sonic Advance series.

Again, you're missing what i'm saying, so let me be clear: Mario is faster in mario games than sonic is in sonic games. While people indeed dispute it, from a per-pixel perspective, Sonic if slower than Mario. Those who play the games extensively will very quickly note that when actually doing a comparison. It's not a doubt that mario can keep up with sonic, but instead a matter of sonic games being slower on the whole. The speed is merely a gimmick, not an actual game mechanic, for sonic. I'd have to do some sort of check, buti don't think mario actually gains speed from these mechanics.

However, what's most important, is the... since i can't think of an english word right now that explains it quite as clearly, イライラ feeling is created by the momentum. This is especially important for the newer 3d games since they run slower because of the transition to 3d (as mentioned in another thread we were in recently). In order to simultaneously make the game difficult while also giving more leeway due to the simulated analog transition, momentum has become necessary for mario games. This is something that sonic games have failed to do properly, and thus it results in odd "takeover mechanics" (in lieu of a better expression) where suddenly gravity or inertia will warp to help sonic make a jump or other motion that he's failing at. Mario's solution was to make all the jumps closer and platforms wider to compensate for the less tight controls, but in turn this can make things too easy, so momentum readds the lost difficulty without ruining the benefits of making platforming more fair for pseudo-analog inputs and collision. That's not to say that momentum wasn't a thing in mario prior to this, but this momentum mechanic appears to be essential for the 3d and 2.5d transition.