Super Mario Bros. 3Xhttp://www.romhacking.net/hacks/1480/


A Super Mario Bros. 3 styled hack, obviously. Adds many new gameplay gimmicks, while retaining the same formula other Mario games have had. It has varying levels of difficulty, but remains extremely fun with tight gameplay and great level design all throughout the hack.
Mario's Amazing Adventure Revitalizedhttp://www.romhacking.net/hacks/3046/


I can't say enough about this hack, and the internet doesn't do it justice. This would have to be in my list of top 3 Mario games I've ever played. It has amazing level design, great music pulled from various games, custom graphics, and just alsjkhlkjghaldkjvn. It is fairly difficult if you want to make it out of the levels before the time limit gets you.
Super Mario Bros. 2 DX


Honestly not much to say about this one. It's a SMB2 remake in the SMW engine. What else is there?
Panic in the Mushroom Kingdomhttp://www.romhacking.net/hacks/48/


This hack is worth playing simply due to its originality! Be warned however that some may find its content offensive. If you are not easily offended, it is hilarious with its use of violent imagery, such as the numerous squirming, bleeding Toads impaled on stakes in a graveyard as shown in the screenshots, not to mention that Morton’s Jail has to be the single most disturbing level ever created for a Mario game! There are also many drug references, a hidden evil Kirby world, and if you can find it, an Adults Only Palace of Hentai. This hack is very fun and is about the same level of difficulty as the original. It features awesome graphics rips, music and overall feel from Super Mario Bros 3, custom blocks, overworld and sprites. Even the credits have something interesting and unexpected in them! So, if you don’t have a problem with some morbid humor and twisted creativity, this is the game for you. Enjoy.
That pretty much says it.