Nope, no protocol for the first mission in a continuum. In most cases, it's not that big a deal, unless it's a continuum that just got de-quarantined or something like that, as in the case of the first Pern mission.

And yeah, if there isn't an OFU, the first person to write about minis in a given continuum gets to decide what they are. Presumably, the mini should be something an OFU could use to keep fanbrats in check and prevent stampeding, so slightly terrifying is good. Usually it's some sort of monster that's unique to the 'verse, though not usually a unique named character, though exceptions exist on all counts.

~Neshomeh