Yeah... my vids have been ignored like 4 times now. Oh well, guess that means everyone's just really busy! :D
First of all, You need to work on:
Spacing
Spacing, basically is, "boxing" your oponent which means attacking your oponent to put him in an akward position, for example, Snake it's really bad on the air, so you have to use Meta knight's attack in order to put Snake in the Air and above metaknight, so Mk can abuse his U-air juggles and air dodge traps (shuttle loop, N-Air).
Ko moves
You need to work on your Ko moves, MK is a weak character in terms of "KO skill", everytime you use an attack it gets weaker, so if you start spaming your D-Smash/N-Air before the oponents gets in a killing range (usually 110/120%) your attack won't kill your oponent! so you have to save your KO attacks for the right moment, and use the right attacks to rack up damage (U-Air, F-Air, Tornado, etc)
Your overall Game
You, basically. need to play more, watch videos of the top players and try to do what they do, most of the time you will learn only one thing of a video, but that little thing will help you greatly, I suggest Watching videos of Mew2king/Anti/Dojo/Seibrik/RedHalberd/Staco/etc. Your overall reaction time is slow, and your "brotherhood" in the game is little, you solve this things by playing a lot and watching your own videos, and figuring what to do in certain situations and stuff.
Your overall game it's not ********, you just need to play more, but i can you give you these tips.
IF you get attacked, just GSL (Grounded Up-b), you will counter that attack and rack up damage
If you are getting attacked from above do a quick Short Hop and do an U-Air (UP+A in the air), this attack has insane priority and its insanely fast
Try to put more "space" between kirby and you, that distance is the distance of your Forward aerial attack and your F-Tilt (tilted control stick, on the ground +A)
I will edit with more information, hope this helps