...of a halfling rogue tumbling through an enemy's square, up steep stairs, in the dark, at full speed?
Using rectal extraction at the table I said -18 to the roll, but I wanted to double check those numbers. Player thought I was being a bit harsh, personally, I was thinking I was giving them a break. Anyway, having a chance to pick through the rules I find:
OK, enemy's square is 5 + CMD
stairs is DC + 4 (pg 415)
blinded is -4 to the check (so, effectively also DC + 4) (pg. 443)
Tumbling at 'full' speed DC + 10. Which is still halved due to difficult terrain (up steep stairs).
So, I still end up with effectively 23 + CMD to tumble 20 feet as a double move.
Blinded moving at full speed also requires a DC 10 to move faster than half speed. (I forgot this but unlikely to matter because said halfling rogue had +20 acrobatics).
Did I miss anything?
Skills don't get nat 20s.
Skills don't get nat 20s.
You can roll a natural 20 on a skill check, it just doesn't automatically succeed. Though it's a common houserule in my experience.
No matter what in a desperate gamble it is still better to give it a shot than too not.
Which is why I gave a very high DC (in this case it was 46 total I think.) As a player, I hate when GMs say 'impossible' so, I always try to give a DC even if it is really high. I was curious what other GMs thought, if I was being unreasonable or it should have been a different DC.
I just pulled the -18 kinda out of thin air (-10 for full speed was easy, but I decided double the "DM's best friend" circumstance modifier for blind and also for terrain; so two times -2 = -4 for each for 'really' difficult). It wasn't until after the game I pulled out the books and checked and was a bit surprised to see that -18 appeared to be exactly the correct modifier.
IMO you did exactly the right thing. Characters should be able to FAIL at super rediculous tasks (like the one you give as an example) until their skill is super rediculous.
A +20 is indeed respectable but it IS a number with a limit. Some things ARE going to be too hard still.
I was using nat 20 for a slang for auto success.
I was using nat 20 for a slang for auto success.
....and the other guy wasn't, yet you assumed he was anyway.