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Character Classes	-	-	-	DMG

The following additional explanations of thief abilities will help you to prevent abuse of these activities by thieves,
and other characters able to use these abilities in whole or in part, in your campaign.

Roll of the dice for any thief function must be kept absolutely secret,
so the thief (or similar character) does not know the results!

Back Stabbing: Opponents aware of the thief will be able to negate the attack form.
Certain creatures (otyughs, slimes, molds, etc.) either negate surprise or have no definable "back",
thus negating this ability.

Picking Pockets:

Failure allows additional attempts.
The victim might notice
    and allow the thief to opercte anyway in order to track him || her back to the place he or she uses as a HQ.
Up to two attempts at picking a pocket can be made during a round.
 

Opening Locks:

The act of picking the lock to be opened can take from 1-10 rounds, depending on the complexity of the lock.
As a rule, most locks will take but 1-4 rounds of time to pick.

<30 points of damage will break open a padlock: T1-4.72>
<another example, 25 points will break a padlock: T1-4.81>
<another example, 30 points of damage will break open a lock: T1-4.49>
<another example, 35 points of damage will break open a lock: T1-4.52>
<condense the above>

Finding And Removing Traps: Use the time requirements for opening locks. <(From 1-10 rounds, though most traps will take 1-4 rounds to find and remove.)>
Time counts for each function.
Small or large traps can be found, but not magical or magically hidden traps.

Moving Silently: Silent movement is the same as normal exploratory movement,
    i.e. 12' per round as the thief creeps up (croodles) upon the AREA or victim or whatever.
Do NOT inform the thief that his or her dice score indicated a lack of success at this attempted stealth,
    if that is the case.
He or she thinks the movement is silent,
    and the monster or other victim will inform the character of his or her misapprehension soon enough.

Quote:
How did you handle situations where a character of one class (say Fighter) was attempting to use Move Silently or Climb Walls - Two situations that when taken literally (i.e. - the Thief can Move with ABSOLUTE SILENCE whereas someone else might attempt to move stealthily, and the Thief can climb SHEER SURFACES wheras someone else might climb a rough cliff, or a tree), would mean that only the Thief could attempt them, but when looked at in a broader fashion, might be allowed for a character of any class ?
 

Generally common sense was applied.
A fighter in metal armor can't move silently, but without that impediment a Dex ability roll with modifiers for surface and/or footwear, would be called for.

Hide In Shadows: As is plainly stated in the PH,
    this is NEVER possible under direct (or even indirect) observation.
If the thief insists on trying,
    allow the attempt and throw dice,
    but don't bother to read them,
    as the fool is as obvious as a cool pile in a ballroom.
Likewise, if a hidden thief attempts movement while under observation,
    the proverbial jig is up for him or her.
Naturally, a creature closely pressed in melee is not likely to bother with looking for some thief not directly in the line of sight,
    but if vision would normally extend to the thief's area of activity,
        then observation rules apply.
Unobserved attempts to hide in shadows must likewise stand the hazard of the dice roll.
A score greater than the required number shows that the character's ability is not on a par with his or her intent,
    and although he or she THINKS hiding has been successful,
    the creature looking in that direction will note a suspicious outline, form, or whatever.
Note also that a thief hiding in shadows is still subject to detection just as if he or she was invisible
(see INVISIBILITY, DETECTION OF INVISIBILITY table).

Hearing Noise:
This is pretty straightforward.
The thief, just as any other character,
must take off helmet or other obstructing headgear in order to press his or her ear to the door surface in order to hear beyond.

see Listening at Doors +
see Hearing Noise +

Climbing Walls: <or: DSG+WSG>

This is probably the most abused thief function,
although hiding in shadows vies for the distinction.
The ability to climb walls is something which is acquired through training && practice,
just as are most of the other functions of the thief.
The rate at which vertical or horizontal movement is possible depends upon the texture and other conditions of the surface.

* SLIGHTLY SLIPPERY surfaces DOUBLE chances of slipping and falling.
SLIPPERY surfaces make chances of slipping and falling TEN TIMES more likely.
Thus, a slippery surface cannot be attempted successfully by any thief under 6th level,
and even a 10th level thief has a 10% chance per round of slipping and falling.

Be sure to check each round of vertical or horizontal movement for chance of slipping and falling.
Surfaces which are inclined inwards move towards greater degrees of difficulty --
a non-slippery one being treated as slightly slippery,
and a slippery one being virtually unclimbable.
Surfaces inclined away from the perpendicular on an outward angle may be treated as either a better surface condition or
a rougher texture, if the degree of incline is sufficient to make climbing easier.

** Most dungeon walls will fall into the fairly rough to rough category.
Some will be non-slippery, but most will be slightly slippery due to dampness and slime growth.

Read languages:
This ability assumes that the language is, in fact, one which the thief has encountered sometime in the past.
Ancient and strange languages (those you, as DM, have previously designated as such) are always totally unreadable.
Even if able to read a language,
the thief should be allowed only to get about that percentage of the meaning of what is written
    as his or her percentage ability to read the tongue in the first place.
The rest they will have to guess at.
Languages which are relatively close to those known by the thief will not incur such a penalty.
 

<note that the original image in the DMG is based on an image by Gustav Dore>