Basically, I'm asking the chances of both sides getting Monotype teams. This happened to me in a Gen 7 Battle Factory match. I got all electric types, and my opponent got all dragons. Does this normally happen, or is it super rare?

You never asked on Smogon, so I did it for you.

Gen 7 Battle Factory chooses randomly from 8 tiers including LC and Monotype, each with an equal chance of being chosen.

Gen 8 Random Battles allow 1 Pokemon of each type combination at most, and 2 sharing a type per team. Monotype teams are impossible and tiers are very balanced with a certain Random chance of devalancing,

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