So, um, recently, I have been watching Ceave Gaming, and in his video of Tips, Tricks and Ideas with the goomba's, he showed a very counter-productive trick that if you hurt a goomba, you die.

Well, firstly, you need to make it forced for small mario.

Secondly, you'll need to make a ceiling out of something that can kill you if you touch it. Spikes will do.
Third, you'll need to make an area 6 blocks down below where you want mario to walk and you can make it use either semi-solids or bridges.

On the 6th row, place a bunch of trampolines, and above it, a bunch of mega goombas.

Here is how it should look like:



Credits to Ceave Gaming who figured this out.