I've made a Super Mario Bros function that adds Mushrooms, Fire-Flowers, Super Leaf's, and other items as well as Goombas, Koopas, warp pipes, and more.
This map is meant as a demo, as well as a way to download the function.
HOW TO MOVE THE FUNCTION TO ANOTHER WORLD
1. Download the map
2. Open Minecraft.
3. Click on the world you want to add the function to but DON'T PLAY IT YET. Instead, click "edit"
4. Click "Open folder"
5. Click data
6. Click functions
7. Go back to Minecraft and click on the world labeled "Yeshuabro Mario Function". Again, DON'T play it yet.
8. Click "Open folder"
9. Click data
10. Click functions
11. Drag the folder "Yeshuabro Mario Function" from the Yeshuabro Mario Function world into the function folder of whatever world you want the function on.
12. Play the world
13. Place down a repeating command block
14. enter "function [tab]" then click "Always Active" and "Repeat", then "Done".
That's it :P Hope you enjoy.
If you have any trouble moving the function to the right folder, feel free to ask. (I usually check the YouTube video more often than the CurseForge post, so if you want questions answered super quickly you should probably try asking them there. If you ask it here don't worry though, I check here often enough. :P)
If you're still struggling, I would suggest reading this Minecraft Forums tutorial I made: