[Antoshi]

If anyone's seen SadisticMystic's Knuckles/Rouge Emerald hunts (I'm sure it's almost everyone here), can you explain to me what he's doing? After he gets an emerald, he promptly kills himself and starts back in the beginning of the level. What does this accomplish?

[Buizel]

SM can explain this better than I can, but basically he's trying to get all 3 emerald pieces close to the start. By dying, you randomize the placement of the pieces that you have not yet collected, but there's a trick to doing this. You can read this to get more detailed information on exactly what he was accomplishing.

[SadisticMystic]

You can't really tell from the cropped videos (well, maybe you can by keeping an eye on the life total), but hunting stages are really tedious to speedrun.  One of the pieces has 45 possible locations, one has 36, and one has 27.  From each of those sets, I only accept the one location that's fastest to reach from the start, so I keep dying until I get each piece where I want it.  In SA1, emerald pieces were treated as checkpoints in both the time and the positional sense.  In SA2, the positional aspect of the checkpoint is removed, so you return to the single start location all the time.  But pieces as "time checkpoints" remain intact.  A good place to observe this is in Pumpkin Hill.
I get the first piece at 4.15, then die shortly afterwards at 4.44.  I end up returning to the starting point, with a timer of 4.15 instead of 4.44.
The effect is more pronounced on the second segment.  The piece is obtained at 8.45, but I don't die until 25.75 (in order to glide to the outer edge so I can set up the rising start, an important timesaver in Pumpkin Hill).  But the piece is the checkpoint, not the kill time, so the clock reverts back to 8.45 for the final segment.  The extra 17 seconds don't count against me at all, and I return to start (albeit not for long, as I get shot upwards).

When you have one piece location, the game looks for nearby locations for subsequent pieces and issues a lockout on those locations, making sure never to put the piece there.  This is to prevent degenerate layouts where all the pieces are in the same spot.  The game doesn't want hunting stages to be that easy.  However, since the lockouts only go in one direction, you can subvert this by getting the pieces in reverse order: 3, then 2, then 1.  I'm not sure exactly what the lockout radius is, but I've done some testing with a possible new strategy in Meteor Herd that involves getting two pieces on the same life.  In terms of probability, the two should coexist once every 1215 tries, but I've spent over 3000 with no success.

Basically, read the guide as pointed out in the previous post.

[Antoshi]

Oh but one more thing. How do you just "know" where a piece is? For example, your run on Meteor Herd, you found two Emerald pieces without them blinking on the bottom? So how can you just tell where a piece will show up like that?

[Buizel]

As SM said, there are 45/36/27 locations where an emerald piece will show up, and SM has mapped out where all the closest ones are.

As for how you know if a piece is where you want it to be: you don't. You just hope that the piece is there, and if it's not, simply die, or, if you haven't collected any pieces yet, Restart (because it's both faster and because extra life capsules regenerate if you restart rather than die.)

(On an unrelated note, I just looked at the New Stats page, and I must tell you that for treasure hunting levels we only count the rings in the level and not rings that were dug up, making your stats invalid. Just thought I'd mention it before a topic shows up on Leaderboard Disputes...)