Ok, new user friendly explanation coming up. I'm going to have to leave certain details out and a few things will have to be generally correct in such a way that you'd never know the difference as I will be trying to avoid saying things that are unnecessarily overcomplicated yet technically absolutely correct. It's going to be dull as hell, but you asked for it. (ho ho ho)
I'm going to call it collectively (for now) Close Quarters Combat (CQC) Z-dropping. There are two distinct and separate ways of performing it, each with their own pros and cons (which are admittedly minor).
How to Perform 1: It's essentially just the Instant Z-drop. Like that's it. Nothing new here. But being new user friendly.... Pull out a bomb, get right up close to the opponent and face them, hit the jump button and then as your character is leaving the ground hit the grab button while your joystick is in neutral. To be precise, you hit the grab button as Link is leaving his jump-squat animation but just before his feet leave the ground, but you won't notice this in real time. If you hit the grab button too early Link will cancel his jump animation and throw the bomb forwards from the ground. If you hit the grab button too late Link will jump, drop the bomb and Zair. If your timing is perfect Link will jump and drop the bomb without Zair coming out. Because you were close to the opponent the dropped bomb will be dropped inside them and immediately explode if they weren't shielding. You are then free to hit them with an aerial or footstool them etc. If you are fast enough, it is in fact possible to re-catch the bomb as it is exploding (known as the 'phoenix bomb'), but don't worry about that for now. If the opponent was shielding when you dropped the bomb they will be able to act immediately but because dropping the bomb is lagless you are technically able to act ever so slightly before them so you can feel free to airdodge if necessary or use an aerial before their move comes out. Also, if they were shielding, the bomb will bounce off their shield and for some unexplainable reason it will still hit them on the way back down and while bouncing on the ground even though it wasn't powershielded.
How to Perform 2. This is basically just a very well timed Z-drop close to the ground, but as before... Pull out a bomb, jump, move Link in the air so that he will land very close to the opponent while facing them, then just before you land, at the very last possible moment, make sure the joystick is in neutral, hit the grab button and immediately let go of the grab button (immediately letting go of the grab button is optional and is simply to make sure you don't shield as soon as you land). If you hit the grab button too early Link will drop the bomb and experience some landing lag such that he cannot act immediately. If you hit the grab button too late, Link will land and throw the bomb forward. If you time it perfectly, Link will drop the bomb on the ground and experience no landing lag and will be able to do anything immediately. Because you landed close to the opponent while facing them, the Bomb will immediately explode if they weren't shielding, and because you landed without any lag this allows you to follow up with whatever you feel like. If they shield the bomb they will be able to act immediately and technically you will be able to act at the same time meaning you will still be able to avoid any option they take by taking evasive manoeuvres or throwing out an attack before they can. Also, if they do shield, the bomb will bounce off their shield and will not hurt them on the way down or while bouncing on the ground.
I guess that'll do. Do you really need a video?