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Ok, here's my take:
Type scramble
Metagame premise: Doubles battle. At the end of each turn, the type of every mon in the field changes in a completely random way.
Potential bans and threats: No bans I could think of. Threats would (obviously) be mons with a sub-par defensive typing and mons...
Speaking of Consolation Prize, I'm in favor of quickbanning the six 100/100/100/100/100/100 mons. They are way too strong and versatile in an OM like this.