Rules are, that we can't edit the sprites, but we can scale and merge them.
What else is allowed to do by us?
The tiles with the blue are suppose to be like that, to look more solid. You can’t change the background filler color on the tiles, you can make the whole tile transparent, but not some of it (this should answer your Mario question) so no partial usage. As for merging, you can overlap but you can’t merge 2 tiles
Hope this helps