Friday, January 18, 2013

The System of Surprise, or, Switzer's Cat


Surprise is an important thing. It's important to gain it, it's important to avoid it.

What is surprise? The usual definition in DND is what it provides in combat - the extra round or more with which one can attack with impunity, often with bonuses.

However, let's look at it another way - let's say some things are more surprising than others. Traps, for example, are built to be surprising - certainly more so than coming upon an orc in a dungeon.

It's not a new idea, a quick Google search presents other folks thinking in the same way. Let's forge ahead anyway.

Switzer's Cat


Who deals in surprise the most? Thieves.

Let's look at the non-magic-related Thief skills and see how they may relate to surprise:


  • Open Locks - Opening a lock quickly and quietly involves being able to gain surprise on what's behind the lock, whether that be monsters behind the door, or a trapped lock (see next).

    A locked door with no opponents behind it is a speed bump in which you can check for wandering monsters or allow an NPC time to act. A locked door containing opponents that can be unlocked in such a way to enforce surprise is worth a roll.

    It's important to note that simply opening a lock in such a way that avoids detection isn't giving an actor surprise on what's inside - it's making sure what's behind the door can't pre-roll surprise, or be granted immunity to surprise because the fighter had to bash down the door. (see Hear Noise, below)
  • Find/Remove Traps - What is a trap? It's a surprise. He's not finding and removing traps - the thief is not being surprised by them.

    Think of Indiana Jones and the Last Crusade, as Indy is talking himself through the traps in the tunnel towards the Grail's vault. He's used up a lot of player agency to have an idea of what's coming. While it was certainly more dramatic for him to kneel out of the way as a penitent man when the blades rush by, an unsurprised thief may just as easily casually leaned out of the way.

    A thief not stating their active attempts to look for traps (however the GM sets that happening) would be considered to have had surprise enforced upon him by the trap instantaneously if the roll fails, or, his levels of experience gave him that last-second Indy Jones style duck-and-weave as the trap springs.

    A thief searching for traps actively (however that's done under GM purview) could be considered to have enforced delayed surprise on the trap. In essence, the trap is surprised, and cannot act before the thief can avoid or nullify the trap. We'd assume here the thief has put himself in danger of being caught in the trap, so that the roll is necessary.

    Going back to Indy, imagine that his attempt to replace the golden idol with the sack of whatever in Raiders worked. He gained surprise on the trap that would have released the boulder, and it couldn't trigger.
  • Pick Pockets - Original source (Greyhawk) has Pick Pocket's percentages combined with Move Silently. That stands to reason - it's about the same thing. You're within encounter distance already, and you're engaging stealth to lift an object.
  • Move Silently and Hide In Shadows - The quintessential delayed surprise mechanic. A thief may resolve the delayed surprise with a backstab, or simply by moving out of the target actor's perception (or waiting until the target actor moves out on his own accord). This surprise is different because you're already within encounter distance - this type of surprise is trumping the easier encounter surprise percentage.
  • Climb Walls - A wall inclimbable by normal means is a trap - the trap is made out of weak handholds, people unexpectedly opening windows, a sudden gust of wind - and when it springs it allows gravity to take you.

    Most people are surprised to fall off a wall they're climbing. However many feet between checks the system calls for, you're checking to not be surprised by that span's "trap". This can just as easily have been you walking across a floor and tripping up on a rumple in the carpet.
  • Hear Noise - This is a lot like a regular encounter surprise roll, but the actor is only using a single, inaccurate sense. You're pre-rolling your surprise roll in regards to whatever creatures you were able to discern with the inaccurate sense - you may still get surprised when you open that door or turn that corner if the reality is markedly different than what you presumed.

So. Take especially the example of Open Lock. It's not a 'skill' anymore - we make no implication that the thief of whatever level won't eventually pick that lock. We only care if he managed to do it in a way that maintains surprise on what's on the other side - be it a monster or a trap he's not setting off with his gentle maneuverings.

We're putting it on the environment - traps are more surprising than encounters. It's harder to surprise someone sneaking up (because you're already within encounter surprise distance). It's easy to miss clues someone's around the next corner (to hear them coming - hearing is an inaccurate sense). The environment itself (a loose brick, a bump in the carpet) is about as surprising as an encounter though.

Now, for all intents and purposes, my post is done. We've reworked what I've seen a lot of forum and blog posts on (regarding thief skills, their descriptions and use) into an extension of the surprise mechanic.

Whether you'd reduce the thief skill percentile tables down into d6, or raise the d6 surprise to percentile (or meet in the middle at d12 or d20, as ASSH and ACKS do) is all up to you.

The fact that it's all the same numbers still makes it all semantics, which is the best kind of change.

But, I've got this shovel and this shallow hole, so let's keep going.

The Cat in Play


Let's list our categories of surprise, then.

  1. A character encounters a target (or targets) for the first time utilizing sight. This is the general start-of-combat surprise.

    This is base surprise.
  2. A passive target that reacts when surprise is gained on the character (or, the character fails to surprise the target). This could be an actual trap (find/remove traps, open locks), or an NPC (pick pocket).

    We'll refer to this as trap surprise.
  3. A character can, through a combination of moving silently, hiding, or other subterfuge (opening a lock or unbarring a door without being detected) impose delayed surprise on a target.

    This is stealth surprise.
  4. A character can use an inaccurate (non-sight, in general) sense to perceive the existence of a target within that sense's range, as in Hear Noise. An animal could just as well use something called Smell Odor. If the situation, when encountered, is close enough to what the character thought he sensed, within GM purview, this surprise roll, if successful, carries into the encounter. If unsuccessful, the character has not perceived the target, so surprise defaults to encounter surprise.

    This will be called indirect surprise.
  5. A character may be tripped up by a slight rumple in a carpet, or, fall to his death after a handhold on a castle wall turns to dust in his hand (climb wall). We'll call this environment surprise.

    As a quick note, I wish Climb Wall could be under trap surprise, but Climb Wall has historically been such a different progression.... I also think I may be able to figure out how to make that an extension of a special-combat-maneuver roll later on.
We've now distilled surprise into 5 separate types. Let's see some examples for each, used in the same manner and form as the thief skills that inspired them.

  • A party moving down a dimly lit corridor, lanterns hooded, turns a bend and encounters a party of cultists doing the same. Base Surprise is rolled for each group.
  • A rogue is working on a locked chest, taking her time and being careful. The GM rolls Trap Surprise for her. She notes the glint of sharp metal above the keyhole and is unsurprised as a poison needle shoots  off to the side of her fingertips - a space where a less canny thief would have left flesh to pierce.
  • A burglar creeps along a battlement at night, moving silently and ducking behind equipment racks and empty pitch-pots to listen for oncoming guards. Indirect Surprise is rolled, and the burglar hears the clank of mail. Stealth Surprise is then rolled, and the burglar nestles in next to a pitch pot, a dark shape in a dark place. As the guard passes, a dagger flies out, the guard drops dead to the floor, the burglar having used her indirect & delayed surprise to stab the man in the heart.
  • A second-story man is scaling a rough brick building, seeking entry through an attic-level shutter. The next brick crumbles under his grip, and making his Environment Surprise roll, he coolly keeps his place, eyeballing his next move a bit more carefully.
  • A fortune hunter listens at the thick ironwood door, rolling Indirect Surprise. Nothing is heard. Not chancing it, he ever so quietly picks the lock - his Trap Surprise roll is successful. He and the man-of-arms accompanying him count down silently from 5 - the armored warrior bursts into the room. The two cultists inside fail their base surprise, while the fighter succeeds, and they are cut down without complaint.


The Cat, Entabulated


OK. So, let's throw out some tables. I'm basing this on Cook Expert as common enough reference, convert as appropriate from your system's thief tables.


I've converted Base Surprise to percentile, here.

Note the second table. That's what happens if you allow someone who's Base surprise is only 1:6 to percolate up to the narrower surprise categories. Useful? Maybe.

I think there's some design space here in moving classes to this system that say "this class is hard to surprise in this manner". For example, let's note the Ranger. Let's say he gets 2 slots to spend on Surprise - he's probably want Base,  Trap, and Stealth. He'll buy Base with one point, and take Trap and Stealth at half a point each, as he'll choose to only have them available in the wilderness. This Ranger would have a base surprise at 1:6, and in wilderness environments, have Trap and Stealth as a thief of his level. (15% and 20% at level 1).

Give the thief 5 points. Maybe he'll drop Environment surprise altogether in order to get a boost to Stealth or Indirect. Any Elf class could take 2 points and take Base and Indirect, to be true to form. A Dwarf could take Trap & Indirect, underground only, then Environment, perhaps. A 3E style Barbarian would take Trap Surprise (they gained a +1 Reflex vs traps every few levels).


The Cat, Combative


Let's convert the above tables to roll-at-on-d20, and add another column, inverting Environment Surprise (which was Climb Walls):


I've called it Combat Surprise. Let's take a page from the DCC RPG, where Mighty Deeds are done. Assume a Fighter takes Base Surprise and Combat Surprise with his two points. At first level, on an attack roll of 20, he's gained Combat Surprise on his foe, and can do something special, perhaps - something on the level of the lowest set of results from DCC RPG's - imposing a -2 to the foe's next attack with a hard parry, knocking the foe back out of melee range with a shield bash, a -2 penalty to the foe's AC next round by knocking it off-balance, some flashy "Are You Not Entertained?" maneuver that rallies flagging henchmen, or declaring some sort of precision strike. Maybe a thief or assassin with Combat Surprise can take a penalty to AC the next round in exchange for some bold maneuver that grants her a backstab against her target.

As in DCC RPG, of course, this only counts if it hits.

As a comparison, the next two tables are a collection of Climb Walls percentages inverted into Combat Surprise, both in roll-to-on-d20 format and percentile chance. The DCC column is the roll-to that the corresponding Deed Die for that level will come up 3, we're assuming the actual attack hit.


So, it's about as likely as falling off a wall, and we can say that literally, since these are the inverted Climb Walls percentages. We're nowhere near the flashiness of DCC combat, but there's a little extra something in there for a good roll. An Astonishing Swordsman in Hyperborea does stay astonishing, though.

Plus it's more entertaining than some sort of max damage/double damage on a natural 20.

So, that's our sixth form of surprise - Combat Surprise. Dangerous in the right hands.

To close, the Surprise table on the regular X-in-6 chances, again using Cook Expert, with Combat Surprise on a d20.  Note Indirect Surprise is an inversion of Cook's Hear Noise. Since we're rolling high, one could take the 1st level numbers and move forward with Skills: The Middle Road instead.







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