We call in Danger Mouse .

As well as many things that are hazardous to the health of agents, there are a few fandoms out there which would probably need special procedures to be followed.

For example, in the Dresdenverse there is an entity that was designed to be a repository for all human knowledge, and magically knows anything that is written down. So agents writing down a charge list as normal might actually tip off a canon character to the existence of the PPC (something which I believe is supposed to be avoided). It could be quite amusing for agents to be forced to charge a Sue from memory, because they don't dare write anything down while they're in the fic.

I'm sure there are various other continua out there that will have odd little things to make agents' lives that little bit more challenging interesting.

Others have covered doing missions in dangerous universes already, but in the case where the Sue herself is extra dangerous (an overpowered God mode Sue) the general approach is to get backup: either bring in Agents that are trained to deal with dangerous opponents (like the DMS Special Operations division or ESAS) or else swarm the Sue with so many Agents she can't resist (e.g the all-agents exorcism of Alumia by DoGA).

Elcalion

The Canon itself is on the PPCers' side. Thus how Agents can derp about in Isengard or a Borg Cube without trouble - they're out of the attention, if not straight-up invisible, to Canon characters who are not in full-on Character Rupture. They also can read the Words, at least until they confront the 'Sue, so they can see huge world-breaking events coming and portal away.

There are quite a few fandoms out there with the potential for risk regarding the safety of the PPC. You've got things like radiation, zombie viruses, brain parasites, doppelgangers, mind control spells, alien races bent on assimilation, and other various sorts of nastiness.

How do we deal with all that? Simple. We don't write about it.

I'm sure we could come up with any number of in-universe reasons for why agents aren't coming down with the Green Flu or getting indoctrinated or what have you. The main reason, I believe, is that writing those stories is something that most people don't want to do.

I wasn't around during the various Emergencies, but from what I've heard they were a pain in the rear to write. After a while, people probably just wanted HQ to remain a safe - if somewhat odd - place. Somewhere stable. Keep the crazy drama to a more manageable (and tolerable) level.

I don't think there are any continuums that are deliberately avoided for being dangerous. Because their authors don't allow fanfiction, yes. But remember: writing missions shouldn't be about going after the most horrendous or most dangerous badfic. It should be about writing the best, most entertaining story YOU can.

PC

Is to avoid the dangerous stuff as much as possible. I mean even in SPC-verse the scientist guys still go around testing stuff. It isn't really dangerous unless you're a D-class personnel.

Also, SCP-173 is nothing. I'd like to see what would happen if SCP-682 got loose. All the weapons in all the worlds couldn't kill that thing.

I don't know, I think that SCP 682 would be worse. Speaking of SCPs, I don't think I've seen very many fanfics for that continuum. Maybe I just haven't been looking in the right place?

Really. Also, pretty much anything can be dangerous. Think about all the canons where someone wants to take over the world. And is shockingly competent at it. It's not just elder gods, eldritch abominations and glitches in reality that are dangerous.

Gurren Lagann: Robots of ridiculous sizes.

Dragon Ball Z: Planets are blown up routinely.

Also, I see your SCP-173 and raise Missingno.