Lately the super mario 3d land modding community has taken off, so they made a discord server to gather and communicate. Nowadays nearly any obj can be imported into mario 3d land as a custom map. Here are just a few examples:
Bob-omb battlefield
Mario Party Intro
and many more imports! But map imports aren't the only thing this discord has to offer! It also offers quick links to a variety of tools and tutorials to help modding and importing that much easier. Custom maps aren't the only mod either, nearly everything can be influenced from the character model to the sound and music!
A link to the discord server can be found Here:
https://discord.gg/015FntJgOKRRPvGlX
(note: i don't own the server, but the owner was so lazy about creating a gbatemp account i decided to advertise it here instead. I did make the logo though)