Would this work...?

Say instead of having to roll under Target Number of X (be it a stat or a difficulty level), instead of modifiying that TN in some fashion, or applying some penalty to the actual dice rolled, the player had to succeed at the same roll more than once. So, in order to do a called shot to someone's noggin, the player not only rolls his under the regular TN to hit someone, but then must roll under it again immediately. If he fails the first roll, he completely misses, if he fails the second he just hits the guy, but not in the head.

I like the idea of this system a lot better than the traditional penalty system, but what is to encourage players not to attempt called shots each round?

Interesting idea, sort of leads you toward a weird dice pool system where all of your dice have to come up successes, and the less dice you roll the better.
The 1st edition of Immortal: the Invisible War sort of did that - you make an attribute check for each additional difficulty (for stuff like wounds or visibility). Different attributes were colour-coded so you could roll multiple checks at once with different coloured dice (blue for the heavy fog, red for the wound penalties). I don't know how it played, though.
 
Theoretically I'd say B.T. is spot on; if you have 2 rolls with a 50% chance of success you end up with a 25% chance of success, so a second roll is fairly harsh, unless your base success chance is quite high.
 
It would however let you apply mitigation of penalties based off various factors really well (as in you can reroll using whatever skill is most applicable - letting you more easily do the equivalent of say varying a called shot penalty based off a guy's Dexterity.
 
Interesting synergy combined with a "Luck Point" type system; if a difficult task requires several good rolls it would involve burning more luck points to pull off.

Quote from: B.T.;517543I like the idea of this system a lot better than the traditional penalty system, but what is to encourage players not to attempt called shots each round?

I don't really know. Two ways: the first, and obvious, is that either the called shot hits or the attack misses entirely.
Or you have some kind of action point initiative system, which wouldn't be my first choice, so that extra rolls such as this cost more points. A straight up attack costs 1 point (for 1 die roll), a called shot (requiring 2 rolls and works as initially described) costs 2.

Quote from: Bloody Stupid Johnson;517545Theoretically I'd say B.T. is spot on; if you have 2 rolls with a 50% chance of success you end up with a 25% chance of success, so a second roll is fairly harsh, unless your base success chance is quite high.

Well, technically, but in most cases I imagine the chance of success on a roll is slightly above average, just to give the player the chance of enjoying himself. I favour the player's odds in game design, just because i think it a friendlier approach.

You could also say that if the second roll is not just successful, but also rolls no greater than the original result then a bonus success happens.

What I might do is: if you roll under your normal to-hit number, you hit with your attack; if you roll under your to-hit number - X, you can choose the location where you hit.

Example: if you're playing WFRP and you have a 50% WS, you need to roll a 50% or lower to hit.  If you roll 30% or below, you can choose the hit location.  Then make a table based on those locations for awesome called shot rules.

Isn't this essentially the Critical Hit system from d20, though?

Quote from: StormBringer;517871Isn't this essentially the Critical Hit system from d20, though?

Basically, although in d20 its only certain rolls that can trigger the confirmation roll. A 19-20 say followed by a successful hit means 10% of successful hit rolls are criticals on average, whereas if it occurs on any roll your critical chance is [chance to hit] x [chance to hit].
 

Quote from: Ghost Whistler;517549Well, technically, but in most cases I imagine the chance of success on a roll is slightly above average, just to give the player the chance of enjoying himself. I favour the player's odds in game design, just because i think it a friendlier approach.

Actually, ignore my complaining about chance to hit being too low. If you needed two rolls to hit that'd be bad, but for a crit you probably don't want too high a success chance.
 

QuoteYou could also say that if the second roll is not just successful, but also rolls no greater than the original result then a bonus success happens.

Roll-under system I'm assuming?
If you need to roll no greater than the first success, then you're approximately halving the chance of the second "confirmation" roll working again.
(If I need to roll between 1 and X to succeed, the average of a successful roll will be the same average as an X-sided dice--half X plus a half). I'm probably not explaining that terribly well, sorry.

Quote from: Bloody Stupid Johnson;517897Basically, although in d20 its only certain rolls that can trigger the confirmation roll. A 19-20 say followed by a successful hit means 10% of successful hit rolls are criticals on average, whereas if it occurs on any roll your critical chance is [chance to hit] x [chance to hit].

Yes, that's true.  I was going off the 20 as a crit, I forgot there were weapons that went as low as...  18?  17?  I don't remember.

The formula holds for any rolls, though.  [first roll odds] x [second roll odds].  Crit on 19-20 = 10%, normal to hit on a 10 = 55%, overall 5.5% odds to successfully crit.  Slightly better than calling a crit on a 20.  Normal to hit on 15+ is a 3% chance for successful crit.

So, I dunno.  Rolling two dice for any kind of check is going to be kind of difficult to figure out while keeping it consistent.

Yup you got it
I love 3E criticals ...the math is something I don't think most 3E players appreciate.

The PHB has weapons that go up to 18-20 (rapier, kukri, scimitar). I think there's a "stump knife" or something somewhere in 3.0 that's 17-20. The 3.0 bladed gauntlet used to be 17-20 as well (led to a couple of Wolverine clones in our games), but this got errate'd somewhere to just 19-20.

It started getting silly when you added Keen and Improved Critical though. And vorpal, back in 3.0 when that worked on any critical