That file you downloaded 'Reborn to Maul' requires a seperate mod as well. If I remeber correctly you need to check the readme to get the link to the origianl Maul skin/model and put that in your base folder along with the 'reborn to Maul' mod.
If you want mods to show up in the "Mods" menu you need to go into your 'gamedata' folder and make a new folder there. Name it whatever you want and then drop the desired mods inside of it. It will then show up under "mods."