The MBG/MBP Unmodded Compilation —
Here I decided to play unmodded on MBG/MBP (modded is default), the only way to accurately do so with default settings is a restrictive method of pressing at most one movement key at a time (this applies to the camera keys too, but I didn't really care about those). This makes a lot of things awkward, anything involving turns becomes hard to do, hence you see mostly simple paths in this video (especially the first half). For full disclosure, I may have held two keys briefly as I switched from one to another (I tried my best to not do those). Hopefully someone can do some coding or something so that the each key will go at 1/√2 of normal speed when two are pressed in the diagonal formation.
A few notes concerning some techniques.
The start pad trick: When doing this unmodded it is not necessary to slow down the marble before hitting the slope of the start pad, as long as you do a close-enough-to-perfect start. I didn't know this for a long time and when I did, I could get 0.01-0.02 better on many of the linear levels.
The jump-jump-jump-bounce-jump-jump start: You see it in at least 2 levels here. It's the closest equivalent to the jump start in MBU that I know of (that can be done easily).
Okay, now to run commentary.
Super Bounce (4.89, 3.68): The first path is the one I used for a while. It was inspired by xboxpro57's Frictional Concerns 6 second path. The second path was one I discovered later. You have to be precise with the bounces or you won't make it over to the finish part. For some strange reason, you can do a more delayed start than this one and you still won't make it over the gap (you'd think it would be the other way around).
Bumper Training (3.07): I use a different bumper and jump before hitting it because that seems to be the only way to get to the finish in a fast time.
Pitfalls (13.02): It's possible to make it over to the top part without any kind of blast, but in this case I need to do a slight run-up at the start, hence my time is about 0.5 off the best MBU unmodded times. Of course some of it could be due to the key press limitation.
Go for the Green (3.92): I remember doing a 4.11 over 3 years ago using about the same path, that was before I could do the level diagonally.
Fork in the Road (4.36): This level was annoying because it was very difficult to do the start pad trick without slowing down. I'm not sure if an edge hit near the end of the level saves time—I know that I think I got it once but finished with another 4.36.
Space Slide (3.31): Beats the modded WRR2 run by 0.01!
Obstacle Course (5.84): I use the start mentioned earlier because that's the fastest way to get to the slope afterwards.
A-Maze-ing (4.21): On my last jump before hitting the finish, I appear to do a light edge hit (which was accidental). In previous attempts I didn't do an edge hit and I wasn't able to reach the finish.
Jump Tutorial (5.50): I thought this path was impossible. I honestly thought it was not possible unmodded and with the key restrictions. I couldn't get the distance after hitting the arch to get to the finish part, no matter what I tried. That is, until I got an accidental edge hit on the part where I do a wall-hit. That changed the path of the marble enough to allow it to bounce to the finish, as you see here.
Learn the Friction! (20.43): The landing after the wall-hit was so much harder than it should have been due to the key restrictions.
Learn the Random Force (4.05): Man was I lucky on this one! Sometimes the trim hit sends you faster than normal. This was one of those times (and with some special sauce on top of that).
Byzantine Helix (9.37): The loop part annoyed the heck out of me since a lot of the time I would do a hard bounce on the start of the second loop instead of a series of smooth bounces, screwing the run. I managed to fix this problem by pulling back as I was nearing the top of the first. Also in my early runs I turned the camera to the right as I moved up the loops. I eventually realized that was completely unnecessary (unlike in a modded run, where you should do some form of diagonal for maximum speed).
Timely Ascent (3.03): If you're wondering, sub-3 is possible (my best catch was 2.98 but I messed up the rest of the run).
Divergence (5.03): I didn't do the trapdoor edge hit not so much because it was harder than the modded version, but because the key restrictions would give me much too poor control over the marble on the rest of the level. That's also why I didn't do levels like Jump jump jump. (I could have just done the part up to the TT, but I chose not to.)
Learning the Basics (10.52): Note the three steps at the top (including the top platform). Normally I land on all three of these, getting a high 10.xx. This time, I was lucky and landed on the first step, then jumped past the second for an edge hit on the third.
Songs: Nightwish - Sleeping Sun, Disturbed - Ten Thousand Fists, and Metallica - The Four Horsemen. The last song is cut off because in iMovie, I compiled one combination video of three Marble Blast videos (this also explains the 0.6 second black screen at the end, that was necessary for the fade to black to not get in the way of the title slide of the next video). The rest of the song covers the other two videos.