Would anyone here know how to adapt titlesets on Mfgg.net made by SuperSledgeBro into Mario builder.

Mfgg.net Made by: SuperSledgeBro
SMAS SMB3 Expanded Fortress / Castle Tileset
SMAS SMB3 Expanded Underground Tileset
SMAS SMB3 Expanded Hills Tileset

I'm looking to used these in the Future for my Mario builder game project that I'm gonna to be working on.

Hi, so I decided to have a look at this, because you seem to be checking the forums still.

To make tileset for Mario Builder, you just have to move tiles around, so that:

• First tile is placed in the top left of the image.
  
• Other tiles are placed, so that each 16 pixels, another tile starts. In the example tilesets below, notice that there are no spaces between the tiles, unless there is a whole 16x16 space of emptiness.
  
• There is an extra row of "empty" pixels. The color of these pixels determines the background color. Notice that the background in the tiles by SuperSledgeBro is white. So I added a row of white pixels at the bottom of all example tilesets.
  

In another words, the tiles are aligned in a 16x16 grid.
The tileset by SuperSledgeBro wasn't aligned in 16x16 as you can see on the image bellow:



To do the aligning, I recommend using MS Paint, especially the selection tool. I saw you mention Paint.NET elsewhere. That's overkill for moving tiles around.

I took the first tileset out of 3 you asked for and turned it into 5 small tilesets as an example.
I left out the purple tiles, because they are here to make your own combinations of tiles, or so it seems.
I can do the other 2 tilesets on the weekend, but I recommend that you try yourself and send your result to learn how to do it yourself. (Send them here, if you do)
Why I did 5 tilesets? So that the tilesets are small and you don't have to scroll as much, when in Mario Builder.

Also to not take as much screen space here on the forums, I placed the tilesets in a spoiler. Just click it to see the tilesets.

The tilesets:

There used to be video tutorials by Ting_Thing, which (I believe) included work with tilesets. With those tutorials deleted off of YouTube, maybe I could do my own tutorials.

I hope it helps.

Thank you also you said used MS Paint instead of Paint.net I will keep that in mind.