Apparently that's not a mask at all; it's a helmet, designed to help Type: Null focus its latent powers at the cost of slowing it down. I'm assuming it can be removed... though we're unlikely to ever see it without the helmet. As for getting one.... well we might be able to snag one later in the story. We sure aren't finding that thing in the wild.Type Null look like an artificial pokemon made specifically for One mission.
And Gladian already has One as his main pokemon.
So , How does Player suppose to catch A Type: Null if its already owned by a trainer ? Unless , There were multiple Type:Null.
Another question ,
How does Type:Null eat ? It has a mask covering his entire mouth .