Clearing up my custom sprites

[LunarCatUSA]

So I made these images for some custom NPCs to add to some horror themed episode. The thing is, the white background still remains. I use paint so I don't know if it's something I need to do with the background or anything like that.

[Emral]

paint doesn't support transparency. Consider using Paint.NET or Gimp.

[LunarCatUSA]

Okay then, thanks!

[LunarCatUSA]

Another question, say I want the Mario model to retain its pixel height in its lowest health form. For instance, my character won’t shrink when he gets hit but just appears more beat up and depressed when he’s at that health. How would I go about doing this? Any script I should look at? Any txt file I should make?