Here is a run of Kirby Super Star that makes use of the game's 2-player capabilities. This was pretty difficult, because I am not two people (and I only have one small keyboard). My aim was still to make this as fast as possible, so I don't use the second player in places where it would only slow me down. There are a few cases where some time is sacrificed for entertainment, however. Note that I use Wheelie Rider kirby a lot, and the helper is lost between games and clearly less important than kirby, so most of the run doesn't look very 2-player.
As the game is divided up into "mini"-games, here's a general description of what I do in each one (mostly about what abilities I used, because that's where the main strategic decisions are):
Spring Breeze: This game mode is very short and simple. I go with the Bomb ability for a helper, and pick up Ice for kirby (note: I make Ice kirby run faster than normal and be partially invincible by tapping the direction to move in every other frame). I take damage at some boss fights to save time and/or sanity. I purposely lose my ability against King Dedede in order to spit it at him as a finishing blow because ability stars do enormous damage.
Gourmet Race: This is supposed to be a race against King Dedede, but I just treated it as a race against time like everything else. Kirby actually handles quite differently in this game mode than in all other game modes, so the fastest way to get around is a little different. (Most notably, fast jumping is possible by letting go of the direction button at the start of a jump). I get the Bird ability in the 3rd race because it flies extremely fast (in this game mode) compared to the other abilities.
Dyna Blade: I grab the Parasol ability at the start because it's actually useful for mobility. (No helper here). I go out of the way for a Super candy that lets me zoom to the end of the level and instant-kill a miniboss in the process. In the next level, I make a helper into a wheelie and ride that wheelie for the rest of this game mode, because that makes Kirby really fast, and amazingly strong thanks to the stars he can snort out when he's riding it (only works with 2 players - wheelie controls movement, kirby controls the stars). I grabbed a Hammer which was kind of unnecessary but it did help kill a miniboss (bug) faster. Thanks to wheelie stars, Dyna Blade barely gets a chance to land. :)
Revenge of Metaknight: This is apparently everyone's favorite mode, or at least it's well-suited for time attacking (besides a few auto-scrolling parts). I inhale 2 ability-giving enemies at once to get Mix -> Wheel for a wheelie rider right from the start. I also went and killed the heavy lobster boss twice (as did Zurreco in his run), despite this wasting a little bit of time. I get the Stone ability for kirby to speed up the 3x wispy woods (I couldn't manipulate Mario, but see if you can spot Samus), then I'm required to get the Flame ability to light a cannon fuse. There are some interesting teamwork opportunities after this. At the final battle with Metaknight, I'm basically required to get the Sword ability.
The Great Cave Offensive: This would be much longer, but I skip all treasures. I get Bird for a little while, then I'm able to Mix a wheelie helper, and again zoom to the end on it.
Milky Way Wishes: In this mode, inhaling enemies to get their ability doesn't work, have to get them (permanently) from ability pedestals. Although there are 2 ways around this (a helper can copy anything by touching it after tapping A a few times, or you can go to a hidden area to get the Copy ability that lets kirby copy anything) I think they would end up being slower. So, I go to Skyhigh first so I can get Wheel for a wheelie rider, which requires I be able to light a cannon fuse so I also pick up Jet (which also turned out to be useful for mobility). with Jet kirby and Wheelie helper, I zoom through the rest of the planets to the end. (Apparently kirby and the helper don't get along sometimes, which you may notice after bosses that take a long time to die...) As if this game didn't already have enough variety (which may be true of this run; sorry for such heavy use of wheelie rider but it's undeniably faster to use it), there is a gradius-type shooter before the final boss. (Also, pay attention before/after the final boss fight...)
I know this run isn't perfect. There are a few obvious (at least to me) mistakes and probably many more not-so-obvious mistakes. It could also be more precise (many actions aren't per-frame optimized) and the 2nd player could have been ignored less. However, overall I think it's still pretty good, and it's definitely a lot faster than the currently published 1-player run. Seeing as how the game is highly non-hex-editable (so I'd basically have to start over to change it) and I've had enough of time-attacking this game (despite how much I like it), I don't intend to go back to improve this anytime soon. I hope you enjoy it, though.
(thanks to Zurreco and samurai goroh for help making this run.)
(EDIT: I should probably mention what mistakes I've noticed I made: (1) In Spring Breeze, I didn't need to give Kirby the Bomb ability, since the helper could've done the bombing until I got Ice. (2) I don't use super-fast climbing for one ladder. (3) I could probably have found some way to manipulate enemies to get Mix in Spring Breeze and/or Dyna Blade. (4) I didn't do a Parasol dash for some reason at one place in a zig-zag part of a Dyna Blade level. (5) When I got the wheel in Dyna Blade, it would probably have been faster to get it from the wheelie shortly before the wheel ability pedestal with the rapid-tap-A-to-die-then-touch-enemy trick. (6) I flapped too fast to gain optimal vertical speed with the bird in the 3rd round of the Gourmet Race. (7) I somehow lost time compared to the other run in the room in Metaknight where I have to light a fuse. (8) I could've done the post-Skyhigh planets in a better order to shorten the trip to Nova. (9) I didn't test if the mine carts in the Great Cave Offensive were faster - they definitely don't seem like it, but I later noticed that they can be controlled with frame precision to give super-speed boosts so it could be comparable after all. (10) I don't think I understand the water physics very well, so I feel that all the underwater parts can be done faster although I'm not sure how.)
Emulator used: the v5 found at:
Forum/Topics/1816
The smv can also be viewed with Snes9x 1.43 WIP1
DeHackEd: Processing