Monotype randbats is a tricky metagame. sometimes winning matchups can become losing matchups over one mon, and sometimes you get a bad matchup to begin with. it's still very much luck based but player skill does matter a lot
Playing random mono is scary especially when you get like rock or ice where most Mon is slow, or when get like poison where this typing almost completely walled by Stell type.
It means all your mons share one type… mono fire means all your mons share the fire type… they will obviously differ in the secondary (or primary) type to actually build a solid team