Declare Fear of Missing Out as an attacker, triggering its ability, causing you to untap it and to get an additional combat phase after this one.
Deal combat damage to an opponent using Fear of Missing Out, triggering Impostor Syndrome, creating a token copy of Fear of Missing Out that isn't legendary.
When the Fear of Missing Out token enters, it triggers, causing you to rummage
During your next combat phase, declare Fear of Missing Out and the Fear of Missing Out token as attackers.
The Fear of Missing Out token triggers, causing you to untap the nontoken Fear of Missing Out and to get an additional combat phase after this one.