i speedrun this game with a focus on the 100% out of bounds category (though currently on an extended hiatus) and i have such a love hate relationship with the collision physics in this game.
The corner clips like the one on the Resort Island rock are possible to do also by wiggling back and forth, but only with Knuckles, Metal Knuckles, Egg Robo or Amy, only on the PS2/Gamecube version, and only in non-snow weather (though ocassionally you can force a corner clip in other circumstances but you have to really try. its only somewhat reliable in the circumstances i mentioned).
There are spots to get out of the level by just walking out at a very precise seam in the wall like the one showed at the wall next to the waterfall in Resort Island in almost every level, but all of them are either useless or slower than the corner clip on the level, though it can still come in handy when youre trying to clip in a situation where you dont have the optimal corner clip setup. So in a speedrun you have to largely rely on the very inconsistent corner clips. Which can vary all the way between getting it within 2 seconds and just wiggling for 1+ minute plus without anything happening.
It's also possible to clip through nearly every wall assuming you have enough speed, which we refer to as slide clip. If you slide along a wall at high speeds and get lucky (or unlucky, depending on the situation), you can pretty much clip out anywhere. Best picks for that are of course Super Sonic or Amy with boost. This basically has become the world record meta for individual level out of bounds runs, you just smack yourself into the closest wall near the start repeatedly until you hopefully clip out. If you're doing an inbounds speedrun and this happens, your run just randomly died.
Once you're out, the game has almost no safety checks to make sure you're actually completing a lap. So you can just line yourself up outside the wall next to the finish line, cross it, turn back around and cross it again, and have a lap time of like 2 seconds. So all 3 lap out of bounds records are only like 10 seconds long.
The looping the finish line works on every track, except Radiant Emerald. Because the track floats so high up, and cause it has a lower path crossing right under the finish line, the finish line trigger doesn't extend to the ground here, so the best you can do is skip part of a single lap and clip back in. Radiant Emerald is also the only track that doesn't have a corner clip or a useful seam clip anywhere. So the only useful way to get out of bounds is by sliding into the wall to the left of you at the start and hope you clip through, which is very inconsistent. My guess is 1 in 20 if you're very good at the drifting technique to maximize your speed. If you manage to get a clip, you can jump from there to the end of the track as it loops back up to the finish line again and ideally do a lap in like 20 seconds or lower. So for a 3lap level run, the holy grail would be getting that on each lap, and cause I don't respect myself or my time, I grinded it out, several times. The first time it took me 96 hours total to get on all 3 laps, though later attempts to replicate it went significantly quicker as I got better at optimizing my slides.
There is one spot in Radiant Emerald that just lets you walk out at a seam, but the way its positioned in the track layout makes it only useful in the Reverse Time Attack version of the level, not in Grand Prix or Forward Time Attack. This is a really cool level run though, and once you get out of bounds, you have to be really careful maneuvering through the void, so that you don't walk under parts of the track that zip you back up on top.
Another weird kinda obscure collision thing I love is, okay, so, when you get a lot of rings, your character gets heavier, and you build up more momentum sliding sideways. With rings infinitely respawning, you can grind all the way until the ring counter maxes out at 999. But once you go over 800, things get kinda... weird. It is very satisfying to do the regular speedrun sliding with a high amount of rings because slides carry ridiculously far and you zoom all over the place. But around that 800 mark, the heaviness of the character starts to massively disagree with the stage's collision model. When you slide around, every couple seconds the game will bump you into nonexistent collisions and bump you backwards, especially on uneven grounds like the banked turns in Radiant Emerald. Visually its really bizarre cause of the high momentum it doesnt really look like a bonk, but you just kinda go very fast, and suddenly you go very fast in the opposite direction in the blink of an eye. While having a lot of rings is useful for inbounds fastest single lap records, maxed out ring counts are very much unusable but still funny and bizarre.
What I'm getting at this game is ridiculous, and I love it a lot
