I'm interested in any advice for running a game with a secretive type nemesis. My group is about to head into a run I've based off of Die Hard. They are breaking into a gov building to install a virus while the only npcs are roughly 20 lower minion lvl civilians they need to take hostage to buy time. One of which will be a total bad ass and slip away and attack when they separate.

I figure this will be treated the same as being in a jungle with a predator hunting the characters but we're all pretty new and looking for advice to prep this scenario. I have floorplans and such but any suggestions on small events that could happen I would love.

If the players are wise they won't split the party if they do, give them hell... have the nemesis move small items of furniture down a corridor he/she knows the PC will walk back down in 10-15 minutes while on patrol maybe?

Have him/her leave messages scrawled on walls or doors. The nemesis could have remote access to the security features of the building, have him cut or resupply power to the lifts/elevators/escalators/lights/security doors/vending machines etc etc Don't just make the nemesis a thug to 'attack once they seperate' this isn't a D&D BBEG which the PCs kill for XP & GOOOOOLD!!! Give the nemesis an agenda, craft it like your own PC, give it an Obligation. Make the Nemesis memorable, not just numbers and dots on a page.

Well since we're modeling off perhaps the greatest action movie ever....

Make their nemesis create problems they must attend to, but remind them that they still need to keep an eye on the captives.

They are installing a virus? Nemesis cuts power, reroutes server connections, and then lays ambushes for when they come to fix things.

Make one of the hostages pregnant and then say that nobody is sure what will happen to her youngling if they stun her into unconsciousness (to avoid them merely knocking out all the hostages while they go fix whatever problem their nemesis has given them)

Make one of the hostages an alien that's immune to stun. Same thing. So that the PCs have to split up.

One of the PCs has to develop a German accent.

For a true Die Hard feel, have the PCs create an event that gives them access from inside the building where they couldn't have before. Like, say it's normally only accessible at a far more heavily armed and guarded facility, but a bomb/missile/whatever explodes and procedure dictates that Command Access is transferred to their building alone?

.......

In all honesty though, are you suuuure you want to run them as the bad guys in this scenario?

Here's why. John McClane could only win by drawing the bad guys out one by one, and then Eliminating them. He did not knock them unconscious to be revived later by their stimpack carrying friends, which is what's going to happen when you have PCs.

The nemesis win condition is going to have to be to merely stop the virus. It can't be "kill all the PCs" because that's a bit brutal.

Just thoughts off the top of my head.

I agree with R5D8, running the PCs as the bad guys in this could cause issues. Even if Jon McClane fails to stop him, picking them one at a time could still result in one or PCs dying, and not all at once too! Stopping the virus could be his main win-condition, while he also tries to get 'side-objectives' that help him towards this goal, such as alerting the police to what is going on in the building so that they can begin a siege on it (and get a straight up fight if needed), though then the question becomes how will the PCs work to stop him from achieving these goals.

A variation could be that the PCs are actually a THIRD faction in all this, they came in to steal the stuff only to find the Rickman lot there too, and now they are in a competition with them to get the stuff first, perhaps without revealing their presence to them at the same time. This way they get to be the McClane squad but instead of trying to be heroes they are thieves too. And the McClane instead tries to get the two groups shooting each other instead of directly attacking them himself.

Also: players will be players. Be aware they may go, "We seen Die Hard too!", line hostages up, and just start shooting them until the guy gives up.