That happens when you throw him straight down, you have to throw him diagonally into the ground to damage him. I hope that fixes your problem.

In order to BG you have to boost with C^ and then grab upwards immediately afterwards (technically both the boost and grab can be in any direction but >90% of the time you will want to do them upwards). The reason you want to grab up and not sideways is cause it has the shortest animation and you need to do them fairly quickly to gain height. The optimal rhythm is somewhere around 4 BGs a second but in reality you probably wanna be a little slower since you just drop the BG entirely if you are too fast. The timing between BGs doesn't affect your speed tho, so if you dont need height you can space them out more. The only thing that affects speed is the time between pressing C and B. You probably wanna hold your right hand above the controller kinda like you would playing on a fighting stick so you can press C with your ring finger and B with your index finger. If you are using another controller you might have to figure out some other method but you certainly wanna use different fingers for boosting and grabbing.

BG example with hand cam:

I'm not a moderator so i can't give a definitive answer but I don't see why it wouldn't be allowed since its doesn't give you an advantage. In fact, some levels actually run at half speed (2-3, 2-8 and the 100/200/400/hurdle disciplines of 3-10 I belive) and you won't be able to use an N64 controller which is pretty much perfect for this game, unless you have a modded one or an adapter of course. As for Emulators, Project 1.6/1.7 is what's used for most other N64 games. The Glide64mk2 video plug-in fixes some graphical bugs but I'm not sure if it's universal or only works with Mupen64plus and it also doesn't fix the slow down. Also, feel free to ask questions about the game/run in general if you have any.

This game has never been released in the west so there is no [EUR] version. He's probably using the japanese version with an an english patch. I tried those things you mentioned with a HD-Display cheat and the capture guru skill. I was able to capture Lagombi with 502/1280 HP, he used 5L+ and 2S (1280-(150¤5+2¤20)=490) so enough to capture him. I tried it a couple of times and the minimum health of Lagombi i got was 1280, the maximum was 1600 so the Lagombi needs to have little health. Same with Wroggi, I captured him with 386/1000 HP (1000-(4¤150+20)=380). On another attempt the Wroggi had 1125 HP and it didn't work, so again he needs to have little health. Making Nibelsnarf fall with 2L+ worked for me. The damage you need to do to make him fall depends on where you hit him. In the video it looks like the bombs hit Nibelsnarf in his mouth. When testing I also hit him in the mouth. I did all of this without bombardier on the [JPN] PSP version.