Becoming a Killer DM: Enough Rope to Hang 'Em

 "H is for Hallways" by Jeff Easley, featured in Michael Curtis' The Dungeon Alphabet

The worthy GM never purposely kills players' PCs. He presents opportunities for the rash and unthinking players to do that all on their own.

Gary Gygax

Running a very deadly game practically requires a lot of player choice, e.g. a sandbox approach.

If you are railroading a party through a series of meticulously planned encounters they had damn well better be balanced.

(Aside: Today, 'balanced' is usually implemented - if not honestly interpreted - as "The PCs will succeed unless the players make fantastically bad choices or rolls". I was brought up differently: When my first AD&D character, a fighter, used a wish to "fight a worthy opponent over a fat purse" (so as to recover his honour with a duel and get some gold), the DM sent a guy actually slightly stronger than my fighter. My fighter died. Ever since, I've interpreted "worthy" as "stronger" and "balanced" as "has a 50% chance of killing you". If I forced my party into a series of really 'balanced encounters' - and without a chance to tip things in their favour through clever play - they'd be dead by the end of the session.)

If you are letting a party run loose in a sandbox, 'balanced encounters' are not much of a concern. As Gygax points out, the idea is to give the players enough rope to hang their characters with.

To wit:

Corridor A opens into a room marked with goblin graffiti and contains a large chest.

Corridor B opens into a room reeking of undeath and features a priceless* gem on a pedestal.

*Okay, not 'priceless'. Let's say 'worth one level each', by the calculations of the thief.

If the players choose corridor B you can run whatever deadly trap or encounter you have prepared. Flood the room with negative energy, teleport a dozen wights into the midst of the party etc. - knock yourself out!

And if the players figure out a way to get their grubby little hands on that gem - and there should be a way, not to mention clues! -, by all means: let them have it and level up. Great risks should yield great rewards.

If you are starting out as a Killer DM, take care to let the players choose which challenges to take on and which to back away from. You'll have far less compunctions about killing off PCs if they chose their own doom.