So I'm wonder what the Acrobatics DC would be on stone stairs slicked with oil. Also do any other penalties apply such as x2 movement? From what I can tell its just DC12 (10 base + 2 slippery)? Or is it considered sloped on stairs? Maybe just treat this as a non-magical grease spell?
And then just on a side note what would happen if the oil caught on fire?
Stairs are normal terrain and would be treated as such unless otherwise specified by the GM (he might decide the stairs are rather narrow, or uneven or something else but unless he does so they are just stairs) but they do increase the DC of any acrobatics check by 4.
If the oil caught fire it would deal fire damage, if there is a lot of it the ground might still be slippery.
I'm going to jump out on a limb here and suggest that what you want is a trap if so I'll rig you up something real quick here:
40 foot slippery stairs that catch fire trap:
Type mechanical; Perception DC 20; Disable Device N/A(20 for fire)
Trigger location; Reset 1d6 rounds 3 times then repair
Effect 40 ft. slide (2d6 non-lethal and prone) 2d6 fire damage; DC 20 Reflex avoids(see special) Fire damage (no save)
If the trap is spotted the slipperiness cannot be disabled but an acrobatics check (DC 16 balance check) can be made instead of the reflex save to avoid falling down the stairs If the reflex save is successful it must be made again each round they are on the stairs (or they may make the acrobatics check instead). If someone is on the stairs for more than three rounds the top stair catches fire which spreads down the steps at the end of the round -- this part of the trap may be disabled.
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Other things you could add in:
Once the fire damage starts it could be smoky causing the balance DC to go up. This smoky might cause the sickened condition on a failed fortitude save, and if you are really devious it could be an inhaled poison too.
Maybe just treat this as a non-magical grease spell?
That's what I'd use as a guideline.
Well originally it was a sort of manual trap where barrels of oil where knocked over the stairs, then the archers at the top would shoot flaming arrows at it and pelt anyone who tried to come up but I like your trap so I'm going to use its rules including making the smoke toxic. Thanks.