In this video, I cover getting all the Teensies and Cups for the "The Mysterious Inflatable Island" level of "20,000 Lums Under the Sea".
Though the level does indeed include an inflatable island, it's not particularly mysterious nor it is really something that seems worth naming an entire level after. It's just another minor quirky addition amongst a sea (ha) of quirky but quickly forgotten things in this game.
0:16 - I found the very first lum spawn here to be quite deceptive. I didn't even realize it was there my first time through because the spawn ended up looking like a sun over the horizon, but when I had difficulty reaching the gold cup requirement I looked harder to see if I missed anything. I think I got nearly all the lums I could in this video, but even then this level does not contain that many extra. Make a serious effort to collect as many purple lums as possible as you might end up short if you get sloppy.
1:23 - The green light / red light stealth dynamic reminded me a lot of stuff like Stealth Bastard / Stealth Inc. I'm not sure if the resemblance is coincidental or purposeful.
1:49 - The lower scuba toad near the cage can be difficult to hit without getting injured, so feel free to skip him so long as you're still doing a good job collecting other lums.
4:57 - As you saw, I made a pretty serious effort to collect as many lums as possible (I think I only missed 5 lums from a single time-sensitive enemy) and I still did not end up with that high of a lum count. 700 - 800 is common for other levels if you really exhaust them of even the more tedious lums, but I didn't crack much higher than 600 even when playing basically perfectly.
In this video, I cover getting all the Teensies and Cups for the "The Mysterious Inflatable Island - Invaded" time trial level of "20,000 Lums Under the Sea".
0:14 - Since the water slows you down already, you should basically ignore every toad that's not directly in your path. You should still be able to fulfill the gold cup requirement even without going out of your way.
1:04 - Hey, we're now officially halfway through the game, at least according to the Teensy count. Can't believe it took over 50 videos to get to that point.