[Continuing the discussion on designing incursions.]
The GM controls the scope. By default, The Infinity Files is a globe-spanning campaign setting. Players travel the globe, looking for current incursions or information and artifacts left behind by previous incursions. (And, occasionally, people. Or monsters.)
However, a campaign can focus only on one locale (the United States, Japan, Australia), and the portals that open there. In this kind of campaign, it’s assumed that other agencies handle incursions in other places. (The EU, for example, may have a team that’s dedicated to investigating European incursions.)
Or, if the gamemaster wishes, he can create a “strange little town” setting. This one town, for whatever reason, is a junction of portal activity. They open and close all the time, and weird things happen to the town on a regular basis. Such a burg can be any small town, even a fictional one, or a major metropolis like New York or Chicago. (Or even something like Nexus: The Infinite City.)
The incursion can be big or small. The default size is a few square blocks, but they can be bigger, encompassing a whole city, state, country, continent, or the world. They can be smaller, encompassing a single street or cul-de-sac, a building or home, or even one single person.
(That strange little street, where all the people are just a little too happy, and wandering pets seem to disappear? Perfect Infinity Files adventure.)
Portals can move. They can relocate across the country or across the planet. If the players defeat it in Manhattan, it can reappear (sometime later) in Hong Kong. Wherever the GM wishes, that’s where a portal can be.
Portals last as long as the GM wishes. Portals are, by default, temporary things. A portal can open to a specific Earth, cause an incident, then close up (on its own, or as a result of player interference). Or it can last for weeks, months, and years.
[Continued in Part VI.]