Like it says. Make your own "What If "(s) for the merry mutants. Feel free to come up with a full scenario for yourself or others What if's.
I'll start:
What if the O5 formed the Brotherhood of Evil Mutants with Magneto while the original Brotherhood became the X-Men?
What if instead of forming the X-Men, Charles Xavier became Black King of the Hellfire Club?
What if only females could be mutants?
What if mutants weren't discriminated, but mutates (all the other super-people) were?
What if Genosha was never destroyed by Cassandra Nova?