Here's the plan: an antagonist for a group of runners who, without 'ware, magic or technomancy, is dangerous enough to make the group reach for their guns at the mere mention of their name.

Now my initial plan was to go the 'Joker' route: Insane, enjoys collateral damage, lots of explosives and poisons, lots of expendable gang muscle who're too fanatic/crazy to run away even when hopelessly outmatched. He wouldn't be a match for the group's combat characters in a straight up fight, but that's what minions are for, right?

Then I thought of the 'Lex Luthor' route: Powerful businessman masterminding a series of black ops that the team manages to get in the way of. someone untouchable, or near enough, who they have to defuse somehow.

Any suggestions of more types of mundanes that can be really scary to shadowrunners, and how to run them?

Batman/Bruce Waye
Iron Man/Tony Stark
Gargoyle/David Xanatos..
Money is the best Super-Power after all.
Does not have to be ware, i think about 80 to 90% of all cyber/bio can be emulated by external gear.
Then there is the faceman, the connection guy who makes life hard for them by finding out what they are up to and then sending other people against them, using his connections to stop their connetions.

A Drone-Rigger works completely without anything built in nowadays.
Same for a Decker nowadays(no, i will not call them Hacker, deal with it <.<)

Find out their secrets yourself, steal their vehicles . . Databomb their network, disable their communications.
Sign their sins up to troll on dwarf gay sado maso porn. be creative!

The main drawback of being completely normal is that you most likely won't stand a chance in a straight up fight... But as someone said, if you find yourself in a fair fight your tactics are worthless.
For a scary mundane villain relying only on himself. Stealth and subterfuge will be rather vital.
A Sniper doesn't need wires, he got time. Someone constantly unseen, but constantly present.

A mastermind plotting in the background, constantly three steps ahead, constantly manipulating. Dr Moriarty springs to mind.

Can probably think of more...
I thought this thread was going to be about Null magicians, colour me disappoint

Mr.Lucky Luke, high edge so the characters will never be rid of him, ever. Combine with some stuff to make him a good shot makes for a mean disturbance.
James Bond is also an idea, if you have the might of the state or corporate behind you and are not afraid to use it to your own advantage, then you can do so much . .

or... *looks over shoulder* the G-man

A rigger needs little or no 'ware, too.

a rigger with an effectively unlimited budget? Yeah, he's bringing a full-on fraggin' BATTLEMECH to that stand-up fight. "I'll see your minigun, and raise with twin rotary assault cannons and quad Shiryu automatic grenade launchers with two thousand rounds of belted ammunition ... EACH. And that's just the LEFT arm ..."

The guy who made "The Bus" had no 'ware or magic at all. Just a really high Explosives (Improvised Explosives) Skill level and Specialization.

*nods*
a Tank-Rigger would work too . .
and with the heimdall drone, why use a bus?

With Calling rules, you don't even need to be awakened to have access to magic also. Not to be used as a primary source of damage or combat prowess, but definitely as a supplement. Guard and Concealment on someone who everyone knows is not awakened may leave the group scratching their heads.

ART DANKWALTHER!

Well, it took a Thor shot, to take HIM out.

But yeah, personally I would go with high log, int, wil and a lot of ressources. Grey eminences (is that a term in English?) are much more threatening than a terminator, in my opinion, and as such business- and / or madmen with an agenda can rapidly climb the ladder of notoriety. Think Keyser Soze.

How about "Kaiser Soze" (don't quote me on the spelling) from "The Usual Suspects". Everyone in the underworld knows the guy's name, and the stories associated with it, but absolutely nobody know who the guy is, or if he's a figment of people's collective imagination.
The guy is super intelligent, a master of manipulation, and has enough connections and clout to make pretty much anything happen, given time to prepare.

Contacts. Dear god, contacts. Set this guy up so that he knows -everybody-, and all their dirty little secrets. He knows where the strings are, and he'll pull them if he has to. Killing him would just start a full-on war as his 'failsafe' distributes what he knows... to the people who can best use it against them.

Gloat about this. Rub it in the players' faces that they can't kill him without hanging themselves out to dry.

They'll probably cap him the first time they meet him.

Better yet! Let him be killed and have the dread come from the chain reaction they started

Contacts and knowledge skills.

The contacts route doesn't work if the character doesn't know how to use them effectively. Conversely, this route doesn't work well against characters who are written up to be socially teflon. Face characters with their own contact networks are a good counter to this approach too. Awakened characters with Divination with Technomancer teammates can also gum up the works. They already know what you have planned and are already 2 steps ahead. (Alpha Mike Foxtrot! )

"I got a bus." *IRAiE Members Run In Terror*

*points at canray*
you are going to need to break some rules to get him right, but if you get canray right, it will be hell on earth for them . . but an interesting hell at least. and so much fun for you.

Well, rules are made to be broken...