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D20 DC Conversion to 1E/Determining Difficulty Level

This tool is particularly useful when using random dungeon generators specific to D20 games

AD&D 1E Conversion By H.J. Martin Adapted from a document by Barrataria
With additional material from conversion documents by G. B. MacKenzie and Rich Franks

"DC" = Difficulty Class

SRD Difficulty Class Examples Corresponding 1E, Basic D&D, D8 Values, roll within the range to succeed. A natural roll of 1 is always a failure. A natural roll of 8 is always a success.
Very easy 0-4 no die roll.
Easy (5-9) 2-8
Average (10-14) - 3-8
Tough (15-19) 4-8
Challenging (20-24). 5-8
Formidable (25-29), 6-8
Heroic (30-39) 7-8
Nearly impossible (40), 8

Suggested usage: The DM consults the narrative, finding a Balance Check of DC 12 (3-8 d8) for anyone running up a slippery stair. Confronted by dangers and forced to fight, a character runs up the slippery stair, perhaps having been duly warned by the DM that the footing is uncertain and that more than walking and that any fighting on the stair would be perilous. The DM (or PC depending on the DM) makes the roll on a d8, allowing for the characters +1 dexterity AC modification, and rolls a natural 1, the character slips on the stair, and plummets to the rocks below, suffering severe falling damage if not death. Had the character rolled 2-8 on the die +1 for dexterity, they would not have lost their footing.

Of course, you can use the 1 to 8 system to determine outcomes in a 1E system as you like. The DM will have to determine what difficulty level the task is and make the roll to determine if the task was successfully accomplished. This can be done per DM choice or by rolling 1d8 and using the result to determine the difficulty. For example, if the DM isn't sure how difficult it would be, they could roll 1d8 with a result of 6. This would put the difficulty of Formidable". The PC must roll a 6 to 8 to succeed. This is not to replace tasks that typically already have a scale of accomplishment such as attacking on a d20 or probabilities already provided for BtB.


Which Dice Do I Use

You'll notice that sometimes some strange dice results will be called for when running a game. for example, swords that do "2 to 7" hit points of damage. Often these results are combinations of dice or dice rolls with additions to them.

Range Dice Rll Range Dice Roll Range Dice Roll
1-2 1/2 d4 3-12 3d4 6-36 6d6
1-3 1/2 d6 3-12 1d10+2 6-72 6d12
1-4 1d4 3-17 2d8+1 7-10 1d4+6
1-6 1d6 3-18 3d6 7-12 1d6+6
1-8 1d8 3-30 3d10 7-28 3d8+4
1-10 1d10 3-36 3d12 9-16 1d8+8
1-12 1d12 4-15 1d12+3 10-40 1d4x10
1-20 1d20 4-16 4d4 11-20 1d10+10
1-100 2d10 as % 4-24 4d6 11-30 1d20+10
2-5 1d4+1 4-26 2d12+2 12-30 2d10+10
2-7 1d6+1 4-36 2d12+2d6 12-48 4d10+8
2-8 2d4 5-8 1d4+4 13-18 1d6+12
2-9 1d8+1 5-20 5d4 13-18 1d6+12
2-12 2d6 5-30 5d6 20-160 2d8x10
2-13 1d12+1 5-40 5d8 21-40 1d20+20
2-16 2d8 5-50 5d10
2-24 2d12 6-24 6d4
3-9 2d4+1


Here's how THAC0 (To Hit Armor Class Zero) works.

Based on a character's experience level, they are able to "hit" opponents of a given armor class by rolling a certain number on a 20 sided die. The lower the character level, the higher the THAC0 will be, making it harder to hit the opponent. The higher the character level, the lower the THAC0 wll be, making it easier to hit the opponent.

So, If a level 1 fighter character has a THAC 0 of 20, and is fighting someone that is armor class 5 they should subtract the armor class of the opponent from 20 and the resulting number,(20-5=15) is what they need to meet or beat to hit the opponent. If the opponent should have a negative armor class, say a -5, then they would add 5 to their THAC0 instead of subtract. In that case, they would need a 25 to hit the opponent. (a natural 20 with modifiers)

Taken from posts by Matthew at Dragonsfoot Forums...

The difference between 1e and 2e THAC0 is that in 2e (as in BD&D) a natural 20 is always a hit and a natural 1 is always a miss. The conversion for 1e is very simple. If you need 20-25 to hit, then a 20 will suffice (as long as there are no negative modifiers to hit). Anything above requires a modifier equal to the number it exceeds 25 by in addition to a natural 20 [i.e. 26 needs 21 (so +1), 27 needs 22 (so +2), etcetera. You don't need the combat tables to run the math, it is pretty simple.

Who Should Use THAC0?

The primary problem with players using THAC0 is that players (and PC's) have no idea what the armor class of their opponents are. Unless, of course, the DM/GM tells the players. I believe that THAC0 is more for the DM's use when rolling on behalf of monsters and NPC's. The DM should know the armor class of the PC's and THAC0 can make melee combat go a bit quicker when rolling for multiple monsters/NPCs instead of constantly looking up combat tables.

I have created a spell called "Know Thy Enemy" recently though that allows spellcasters to magically "know" who or what they are fighting and what the AC of the opponent is.

Fighters Errata


Clerics Errata

Thieves Errata

Pick Pockets

From DragonsFoot "Footprints" magazine, come these tables to help determine what comes to hand from a Thief plying their skills.


Table I: Human, Demi-Human Pocket Possessions

d% Roll Result d% Roll Result
01 Whetstone 02 Rind of Cheese (01-60 Edible, 61-90 Edible but rancid, 91-00 Inedible)
03-10 Coins (See Coins Sub-table) 11-12 Gems (See Gems Sub-table)
13 Small Mirror 14 Jerked Meat (See Meat Sub-table)
15 Flute 16 Scissors
17 Sewing Needles 18-20 Ring (See Ring Sub-table)
21-22 Jewelry (See Jewelry Sub-table) 23 Spell Component’s (DM’s discretion, preferably something slimy)
24 Iron Spike 25 Iron Rations (1 day)
26 Tinderbox 27 Small Knife
28 Roll of Twine 29 Whistle
30-34 1d6 Dice 34-35 Playing Cards (50% chance complete set)
36 Pipe and Tobacco Pouch (10% pipe is inlaid with mother-of-pearl, 1d8 gp value) 37 Candle (tallow)
38-42 Comb (10% made of silver/mother-of-pearl, 2d20gp value) 43-45 Brush (See Comb)
46 Bottle of Ink 47 Quill Pen
48 Fishing Lure 49-52 Writing (Use Writing Sub-table)
53-55 Candle (wax) 56 Small Book (DM’s discretion)
57-67 Empty 68 Trap (See Trap Subtable)
69-70 Small Animal (See Small Animal Sub-table) 71-73 Hairpins (10% precious metal, 1d20 gp value)
74 Herbs 75 Rabbit’s Foot
76 Small Sack (50% chance holds 1d4 items from this table) 77 Oil Flask
78 Holy Water Flask (25% Unholy Water) 79 (Un)Holy Symbol (DM’s discretion)
80-81 Flint and Steel set 82-84 Parchment/Vellum (Blank)
85-87 Perfume (See Perfume Sub-table) 88-90 Handkerchief (5% chance silk, 1d4 gp value)
91-92 Candy (1d4 pieces) 93 Silverware (1d3 gp value)
94-96 Flask of Alcohol (See Alcohol Sub-table) 97-98 Lint
99 Potion (See Potion Sub-table) 00 DM’s Choice


Table II: Humanoid and Monster Pocket Contents

d% Roll Result d% Roll Result
01-06 Meat (See Meat Sub-table) 07-09 Cheese (01-40 Edible, 41-60, Edible but rancid, 61-00 Inedible)
10-12 Flask of Alcohol (see Alcohol Sub-table) 13-14 1d6 Dice
15-17 Small Sack (50% holds 1d3 items from this list) 18-19 Bone Totem (DM’s discretion)
20-22 2d8 Teeth 23-24 Small Mirror
25-27 Set of Playing Cards (incomplete) 28-31 1d3 miscellaneous bones
32-33 Small Monster (See Small Monster Sub-table) 34-35 Hard Tack
36-37 Coins (see Coins Sub-table) 38-39 Gems (See Gems Sub-table)
40-41 Jewelry (See Jewelry Sub-table) 42-43 Interesting yet Worthless Stones
44-45 Flask of Oil 46-47 Flask Unholy Water
48-49 Unholy Symbol (DM’s discretion) 50-51 Tinderbox
52-53 Whistle 54-56 Vile, Disgusting Contents (Save v. petrification or suffer the effects of a Stinking Cloud spell for 1 round)
57-67 Empty 67 Bunch of Flowers
68-69 Tobacco (Chewing) 70-71 Pipe
72-73 Whetstone 74 Very Small Rocks
75-77 Lint 78-79 Iron Rations (1 day)
80-81 Colorful Shards of Glass 82-83 Trap (See Trap Sub-table)
84 Worthless Glass Beads 85-86 Small Knife
87-88 Shrunken Head (DM’s discretion) 89 Ball of Twine
90 Ball of Wax 91 Shears
92-93 Flint & Steel Set 94-95 Flask (empty)
96-97 1d3 Candles (tallow) 98 Potion (See Potion Sub-table)
99 Vial of Acid (See Acid Sub-table) 00 DM’s Choice


A. Acid Sub-table

Such substances are always found in glass containers. The damage figures following the acid description indicate how much damage the fluid inflicts on a direct hit or a splash (see DMG, p. 64).

d% Roll Description
01-25 Very Weak (0 hp/0 hp)
26-51 Weak (1 hp/0 hp)
52-75 Moderate (1d4 hp/1d2 hp)
76-86 Strong (1d6 hp/1d3 hp)
86-98 Very Strong (2d4 hp/1d4 hp)
99-00 Strongest (2d6 hp/1d6 hp)


B. Alcohol Sub-table

Roll on each of the following sub-tables; once for the type of the container, a second time for the contents. For game purposes, consider each container to hold one pint of liquid

d% Roll Container d% Roll Description
01-20 Skin 01-25 Beer
21-40 Ceramic 26-40 Wine
41-61 Tin 41-61 Whiskey
62-70 Cystal 62-81 Brandy
70-75 Glass 82-91 Mead
76-00 Steel 92-00 Grog


C. Coin Sub-table

Roll on each of the following sub-tables; once for the number of coins stolen, a second time for the type of coins.

d% Roll Number of Coins: d% Roll Type(s) of Coins:
01-33 Solitary (1) 01-15 Wooden (worthless)
34-45 Paltry (1d3) 16-50 Copper
46-74 Fair (1d6) 51-76 Silver
75-95 Wealthy (1d10) 77-87 Electrum
96-98 Rich (2d10) 88-98 Gold
99-00 Filthy Rich (3d10) 99-00 Platinum

NOTE: There is a 2% chance that any coins stolen, except for wooden, are counterfeit, being, in fact, brass (worthless) coins.


D. Gem Sub-table

Roll on each of the following sub-tables; once for the number of gems found, a second time for the type of gem(s), and a third time for the base value of the gem(s).

d% Roll Number of Gems d% Roll Type of Gem d% Roll Value of Gem
01-55 Solitary (1) 01-35 Quartz 01-40 10 gp
76-95 Wealthy (1d6) 56-65 Amethyst 61-70 50 gp
96-99 Rich (2d4) 66-75 Amber 71-80 100 gp
00 Filthy Rich (2d10) 76-85 Pearl 81-90 250 gp
86-95 Opal 91-95 500 gp
96-97 Ruby 96-99 750 gp *
98-99 Sapphire 00 1000 gp *
00 Diamond

'*' At the DM's discretion, if the gem type is determined to be 01-75, the stone may be found in a valuable setting that, combined with the stone(s), totals the value determined.


E. Jewelry Sub-table

Roll on each of the following sub-tables; once for the number of items of jewelry found, a second time for the type of jewelry, and a third time for the value of the jewelry.

d% Roll Number of Items d% Roll Type of Jewelry d% Roll Value of Item
01-55 Solitary (1) 01-33 Bracelet 01-35 25 gp
56-75 Fair (1d2) 34-55 Brooch 36-55 50 gp
76-95 Wealthy (1d3) 56-75 Earrings (set) 56-75 100 gp
96-99 Rich (1d4) 76-85 Necklace 76-85 250 gp
00 Filthy Rich (2d3) 86-90 Pendant 86-95 500 gp
91-99 Ring 96-99 1000 gp
00 Tiara 00 2000 gp


F. Meat Sub-table

=---------- d% Roll ----------
Human/Demi-Human Humanoid/Monster Description
01-33 01-20 Fowl
34-55 21-35 Mutton
56-65 36-45 Venison
66-80 46-55 Pork
81-90 56-65 Beef
91-98 66-75 Wild Game (DM’s discretion)
99 76-80 Other Animal (DM’s discretion)
00 81-85 Monster (DM’s discretion)
86-95 Humanoid or Demi-Human
96-00 Human


G. Perfume Sub-table

Perfume is always found in either a glass (70%) or crystal (30%) container. For game purposes, consider each container to hold 1 fluid ounce of perfume (8 drams). Only one container of perfume will be pocketed.

d% Roll Description and Value
01-10 Foul (1 sp.)
11-46 Fair (1 gp)
47-75 Good (5 gp)
76-90 Excellent (20 gp)
91-99 Magnificent (50 gp)
00 Wondrous (75 gp)


H. Potion Sub-table

Roll on the following sub-tables, once to ascertain the type of potion container, a second time to ascertain the type of potion. Only one potion will be pocketed.

d% Roll Container Type d% Roll Potion Type
01-35 Glass 01-25 Healing
36-65 Crystal 26-40 Extra-Healing
66-80 Ceramic 41-50 Philter of Love
81-90 Copper 51-60 Sweet Water
91-00 Steel 61-70 Speed
71-80 Invisibility
81-90 Gaseous Form
91-00 Flying


I. Small Animal Sub-Table

Note that only one small monster of the indicated type will be found. There is a 75% chance that such creatures, when found, are held captive in a small pouch, box, etc.

d% Roll Description
01-10 Mouse
11-20 Canary
21-30 Dove
31-40 Rabbit (Hare)
41-50 Rat
51-60 Bat
61-70 Squirrel
71-80 Frog (Toad)
81-90 Newt
91-00 Snake (non-venomous)


J. Small Monster Sub-table

Following the description of each small monster is the publication in which it appears. MM = Monster Manual, FF = Field Folio, MM2 = Monster Manual II. Note that only one small monster of the indicated type will be found. There is a 75% chance that such creatures, when found, are held captive in a small pouch, box, etc.

d% Roll Description
01-18 Galltrit (FF)
19-35 Goldbug (FF)
36-40 Pernicon (FF)
41-55 Bookworm (MM2)
56-70 Minimal (MM2)
71-85 Webbird (MM2)
86-00 Stirge (MM)


K. Ring Sub-table

Generally, only one (worn) ring can be pocketed at a time.

d% Roll Description and Value
01-33 Wrought Silver (25 gp)
34-50 Wrought Silver and Gold (50 gp)
51-75 Wrought Gold (100 gp)
76-85 Platinum (125 gp)
86-90 Silver with Gems (150 gp)
91-98 Gold with Gems (200 gp)
99-00 Platinum with gems (500 gp)


L. Trap Sub-table

In the event a trap is indicated, the thief should be permitted a saving throw versus petrification, or suffer the listed ill effect.

d% Roll Description and Effect
01-40 Mousetrap (1 hp damage)
41-60 Chinese Finger Prison (hold immobile)
61-70 Small Blades (1-2 hp damage)
71-85 Needle and Dye (1 hp., finger/hand dyed blue)
86-90 Needle and Poison (1 hp, save versus poison or be slowed for 1d4 turns)
91-95 Needle and Poison (1 hp, save versus poison or be paralyzed 1d4 hours)
96-99 Needle and Poison (1 hp, save versus poison or suffer 3d10 hp damage)
00 Magic Mouth spell (on small item in pocket) shouts, “Thief! Pickpocket! Help!”


M. Writing Sub-table

At the DM’s discretion, a purloined writing may lead to other adventure leads, including blackmail and extortion.

d% Roll Description
01-33 Love Poem
34-45 Deed to Real Property
46-50 Writ from Local Magistrate/Lord
51-55 Spell Component List
56-70 Common Correspondence
71-80 Official Correspondence
81-90 Map
91-95 Treaty
96-00 Treasure Map (DM’s discretion regarding veracity)


Magic Users Errata

Magic Item Creation

One of the most common methods of creating an enchanted item is to first enchant the item, then cast the appropriate spell(s) upon it. Depending on Magic user or Cleric, this could go a couple of different ways.


For a Cleric to enchant an item, first they must create a sanctified area. Within that area, they petition their deity to Bless the item in question. Having accomplished that, the item must then have the specific spell desired prayed for to be placed on it. If it is to be a multi-charge spell, it must have as many spells cast upon it as charges it is intended to have.

All in all, it takes 1d4 days to create a sanctified area, then another 1d4 days to bless the item IF the deity has decided to Bless the item at all. The cleric has a 5 to 15% chance that the deity will Bless the item, each day, gaining 5% chance every day attempted/prayed for afterward. I add in that if a natural roll of 95 to 100 then it is automatically blessed with no further prayer required and that any spells cast upon it will be doubled in strength. Conversely, if the roll is a natural 1 to 5 then the item is permanently refused to be blessed and no attempt to cast spells upon it will work.

A cleric may re-charge the item, if it is re-chargeable, by creating a sanctified altar area as described above then casting the number of spells per number of charges it is requested/able to hold. The ability to cast a certain number of spells upon the item is directly related to the Cleric's level and ability to cast a certain number of spells per day.

See the 3rd level homebrew "Altar" spell to create sanctified area and "Commune" 3rd level Cleric spell to ask deity to Bless item.

It is advised that Clerics should collect a fee or "donation" for creating an enchanted item that is 500 GP per day required to create the item and a minimum of 500 GP per level of spell being cast upon an item. If a multiple charge item, then 500 GP per level of spell multiplied by the number of spells/charges cast upon it.

In the case of recharging, the fee should be 500 GP per level of spell multiplied by number of spells/charges placed upon it.

Magic User

Monsters Errata

Hit Dice

When consulting "Appendix E: Alphabetical Monster Listing" in the Dungeon Master Guide, you will note that "Hit Dice" will tell you the number of hit dice to roll to obtain the monsters Hit Points but does not tell you what # sided die to roll. In AD&D 1E, All monsters roll a d8 unless otherwise specified.


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