Okay, I just found a 1-up glitch in level 1-3 of SMB3.
Around the midpoint of the level, you have the dark brown winged Goomba, like so:
Using the feather, stomp on him twice, then quickly fly over and stomp out his buddy, then fly over and stomp the Boomerang Brother, all without hitting the ground. If you do this right, the scores for the enemies will go 100-200-400-800-1UP. Yes, you heard me right, a 1UP off only five kills instead of 9 (100-200-400-800-1000-2000-4000-8000-1UP). Note that if you have the momentum to make it to the row of Goombas on the next screen, they'll be 2000 and 4000 if you hit them (so it goes 100-200-400-800-1UP-2000-4000-8000-1UP).
I think this glitch may be due to the fact that killing a Boomerang Brother gets 1000 points.
