Hi there!

these images are from Maple Story (The popular game),

I wanted to know ( I tried to ask a lot of people nobody knows ), What are these mobs designs? 

Are they pixel art? vertical art (made with illustrator)? made with photoshop? inkscape?

Please let me know as soon as you can & if you can direct me to some guides to this specific design tutorial I'd much much appreciate it! :)

Thanks so much for even taking your time to read this!

This is not a Game Design question. Moving to 2D and 3D Art forum.

9 hours ago, yonisit said:

Are they pixel art? vertical art (made with illustrator)? made with photoshop? inkscape?

It is raster(as in made from pixels) made with any digital paint software. Photoshop, Gimp, Krita all will do this easily.

This isn't any special style, the artist just opened there 2D software and made art; making their own personal style. Probably with a small brush that had no smoothing, to get the pixelated look.

The black edges looks like a shader, because it is exactly 1 pixel thick, and looking at the game it doesn't sample when rotated.

The smaller art in Maple Story IS pixel art. That is why characters stand out so much.

9 hours ago, yonisit said:

Please let me know as soon as you can & if you can direct me to some guides to this specific design tutorial I'd much much appreciate it! 

If this is really ASAP then you should hire the original artist, or a artist of a similar skill level.

The top group of images will take two years of daily practice to reach that level of shading and shape understanding. The lower images could be achieved with a few months of practice.

The edge shader should be very simple and basic. Something that copies the image and moves makes it black, then moves it around to get exactly 1 pixel.

Good ole' Maple Story.  

Here are some links to help learn pixel art:

http://makegames.tumblr.com/post/42648699708/pixel-art-tutorial

https://www.hongkiat.com/blog/pixel-art-tutorials/

https://lospec.com/pixel-art-tutorials

Like @Scouting Ninja said, it will take some time to get to that level, but it all depends on your natural talent, skill and ability while learning.