Negative levels!

I encountered an level negative 153204 divine arecus in a random battle, and it was awesome. Even though all it had was struggle... that could 1 hit ko anything and all damage (EVEN RECOIL!) gave extra health...

Please, if you figure out how, please edit this to show how to get to levels 0 and under.

Although, this was modded. But i cannot even level down a pokemon with common candy down to level 0