Maybe You got the frame perfect trick? Which allows you to enter doors with an item?

Had to be a first-frame grab since it's the only way to perform this glitch (that I know of). You get this by grabbing an item on the very first frame when a screen loads. The trick can be seen performed in top runs in 1-1 and 1-2.

"i also picked up an onion instead of a 1-up"
If you had already grabbed the 1-up, it'll become an onion after that