Tuesday, August 19, 2025

OSE to Mothership Conversion

 So, I had an idea of converting between OSR and Mothership. Like those giant and dubious 3rd party booklets they used to sell. Or the weird part-adaptions Deadlands used to put in its crossover books.

But I didn’t know how it would work in practise, so I ran through three different iconic and tiered monsters from OSE and saw which version worked best.

My version was what I compiled by myself; Hundreds is the page from the book HUNDREDS by Paradiso (Warped Beyond Recognition) and Hull Breach has published its own character conversion, one that is designed for Stars Beyond Number.

 

ORC

Armour Class           6 [13]

Hit Dice                     1 (4hp)

Attacks                      1 × weapon (1d6 or by weapon)

THAC0                       19 [0]

Movement                120’ (40’)

Saving Throws         D12 W13 P14 B15 S16 (1)

Morale                       6 (8 with leader)

Alignment                 Chaotic

XP                                10 (leader: 10, chieftain: 75)

Number Appearing 2d4 (1d6 × 10)

Treasure Type           D

________________________________________

•                                   Hate the sun: -1 to-hit in full daylight.

•                                   Weapons: Prefer axes, clubs, spears, or swords. Only leaders can use mechanical weapons (e.g. crossbows, catapults).

•                                   Craven: Afraid of larger or stronger-looking creatures, though leaders may force them to fight.

•                                   Leader: Groups are led by an orc with 8 hit points. The leader gains a +1 bonus to damage rolls. Leaders have defeated other orcs in combat to gain their position.

•                                   Orc chieftain: A 4HD (15hp) chieftain rules an orc tribe. The chieftain gains a +2 bonus to damage rolls.

 

TROLL

Armour Class           4 [15]

Hit Dice                     6+3* (30hp)

Attacks                      2 × talon (1d6), 1 × bite (1d10)

THAC0                       13 [+6]

Movement                120’ (40’)

Saving Throws         D10 W11 P12 B13 S14 (6)

Morale                       10 (8 fear of fire)

Alignment                 Chaotic

XP                                650

Number Appearing 1d8 (1d8)

Treasure Type           D

________________________________________

•                                   Regeneration: 3 rounds after being damaged, start regaining 3hp per round. Severed limbs reattach.

•                                   Return from death: If killed (0hp), will regenerate and fight again in 2d6 rounds.

•                                   Fire and acid: Cannot regenerate damage from these sources. The only way to permanently kill a troll.

•                                   Fear of fire: Morale 8 when attacked with fire or acid.

 

RED DRAGON

Armour Class           -1 [20]

Hit Dice                     10** (45hp)

Attacks                      [2 × claw (1d8), 1 × bite (4d8)] or breath

THAC0                       11 [+8]

Movement                90’ (30’) / 240’ (80’) flying

Saving Throws         D6 W7 P8 B8 S10 (10)

Morale                       10

Alignment                 Chaotic

XP                                2,300

Number Appearing 1d4 (1d4)

Treasure Type           H

________________________________________

•                                   Breath weapon: 90’ long cone of fire.

•                                   Language and spells: 50%; 3 × 1st level, 3 × 2nd level, 3 × 3rd level.

•                                   Sleeping: 10%.      



My Version for OSE

HD = Wounds

HP = Health, if HP is under 10, add +1d5+6 (Allowing 1 HD monsters to have between 11-15 Health), add the OSE HD modifier to Health if average not listed.

At the Warden's discretion, really small animals can just keep the HP as Health for being fragile.

If 4 Wounds or higher, deduct 2 Wound and 10 Health for every 3 total Wounds.

If this reduces the new Health total to less than 10, deduct 1 Wound from the total amount and add 15 to the Health.
If the Warden does not like the high Wound and low Health end result, they can halve the Wounds and double the Health.

Combat = 21 -THACO + Any listed modifiers x5 +15, or Ascending Attack Bonus +2 + Any listed modifiers x 5 +15.

Instinct = HD x 10, becoming HD x 5 after 5 HD, as a percentage

(9-AC/AC-10 for Ascending) round down = AP

d4 = d5

d6 = d10

d8, d10, 2d6 = 2d10

Doubling as you go

Once you get to 4d10, you have the option of changing it to 1 Wound if caused by massive damage.

Bonuses to damage are ignored unless they are +2, then up the dice by one per +2 on the chart prior to converting.

If a + Weapons is required to hit the monster, deduct 1d10 from the damage of the Mothership weapon per + required.

 

HUNDREDS

Many entries are already system-agnostic and require no adaptation for use with other systems, but some that make reference to specific mechanics, damage values, etc. may require some adjustment. When adapting entries to other systems, take the following into consideration (rough conversions listed are from Mothership to a generic d20 system with 3d6 stats, hit dice, etc.):

ARMOR in Mothership 1E is rated in Armor Points (AP), and ranges from 1 (clothing) to 10 (heavy armor). AP is subtracted from incoming damage, and if the incoming damage exceeds the AP, the armor is ruined.

– AP 0 ~> Unarmored

– AP 1 ~> As Cloth

– AP 3 ~> As Leather

– AP 5 ~> As Chain

– AP 7 ~> As Half Plate

– AP 10 ~> As Full Plate

[+] AND [-] are Mothership shorthand for rolling with advantage and disadvantage, respectively. Advantage: roll twice and take the better result. Disadvantage: roll twice and take the worse result.

DAMAGE in Mothership generally ranges from 1 DMG (foam gun) to 4d10 DMG (shotgun at close range, smart rifle).

– 1 DMG ~> 1 HP

– 1d5 DMG ~> 1d4 HP

– 1d10 DMG ~> 1d6 HP

– 2d10 DMG ~> 2d6 HP

– 3d10 DMG ~> 3d6 HP

– 4d10 DMG ~> 4d6 HP

CHARACTERS HAVE MAX WOUNDS

in addition to HP in Mothership. When they lose all their HP, they gain a Wound, and their HP recovers. When a character suffers their Maximum Wounds, they die. An average player character has 15 HP and a maximum of 2 Wounds. NPCs and many Horrors just have Max Wounds (any damage taken just deals a Wound instead).

– 1 Wound ~> ½ HD or 1 HP

– 2 Wounds ~> 1 HD

– 3 Wounds, etc. ~> 2 HD, etc.

CHARACTER STATS in Mothership are Strength, Speed, Intellect, and Combat, which are all values ranging 0–100, but 36 is average. Character saves in Mothership are Sanity, Fear, and Body, also ranging 0 – 100, averaging just 21.

– Strength ~> Strength, Constitution

– Speed ~> Dexterity

– Intellect ~> Intelligence, Wisdom, Charisma

– Combat ~> Whatever you check to attack

– Saves ~> Use whatever save is closest

NPCS AND HORRORS in Mothership usually only have Combat and Instinct stats. Instinct acts as a catch-all for any unlisted stats and saves. Hired Contractors also have a Loyalty save determined after the PCs hire them.

– Stat/Save of 0 ~> Stat of 0, 0% Save

– Stat/Save of 25 ~> Stat of 5, 25% Save

– Stat/Save of 50 ~> Stat of 10, 50% Save

– Stat/Save of 75 ~> Stat of 15, 75% Save

– Stat/Save of 90 ~> Stat of 18, 90% Save

 

Hull Breach Conversion Document

"HD ÷ 3 = Wounds

HD × 3 = Health

Skills Bonus × 20 = Instinct [+/-10]

Atk Bonus × 5 = Combat

Total DMG = DMG as d10s [+1d10]

AC ÷ 3 = Armor"

 

 

My Version

ORC

1 Wound

Health 11-15

Combat 25%

Instinct 10%

AP 3

Attacks 1 × weapon 1d10

Combat 20% in full daylight or similar.

Leader: Groups are led by an orc with Health 15-19

 

Orc chieftain

2 Wound

Health 20

Combat 40%

Instinct 40%

AP 3

Attacks 1 × weapon 2d10

Combat 35% in full daylight or similar.

 

 

HUNDREDS

ORC

2 Wounds

4 AP

Attacks: Combat 1 × weapon 1d10

Combat 50% [A To Hit value of 0 means a score of 10 which converts as 50%]

Instinct 50%

Hate the sun: Combat 45% in full daylight or similar.

 

Leader: Attacks 1 × weapon 1d10+1

 

Orc chieftain

4 Wounds

4 AP

Attacks: 1 × weapon 1d10+2

Combat 50% [A To Hit value of 0 means a score of 10 which converts as 50%]

Instinct 50%

Hate the sun: Combat 45% in full daylight or similar.

 

Hull Breach Conversion Document

ORC

Wounds 1

Health 3

Combat 10% [Cannot use Ascending bonus x 5 as its 0]

Instinct 20%

2 AP

Attacks 1 × weapon (1d10)

Hate the sun: Combat 5% in full daylight or similar.

Leader: Attacks 1 × weapon (1d10+1)

 

Orc chieftain:

4HD

Wounds 4

Health 12

Combat 15%

Instinct 30%

2 AP

Attacks: 1 × weapon (1d10+2)

Hate the sun: Combat 10% in full daylight or similar.

 

My Version

Troll

4 Wounds

10 Health

Or 2 Wounds and 20 Health

Combat 55%

Instinct 55%

5 AP

Three Attacks every round

2 x Claws 1d10 Bite 2d10

3 rounds after being damaged, start regaining 3 Health per round. Severed limbs reattach.

Return from death: If killed Wounds are 0, will regenerate and fight again in 1d10 rounds.

Cannot regenerate damage from fire or acid. The only way to permanently kill a troll.

Instinct [-] or flee when attacked with fire or acid.

 

HUNDREDS

Troll

AP 6

5 Wounds (Could Assume 13 or 18 Health if needed)

Attacks 2 × talon (1d10), 1 × bite (2d10)

Combat Not Stated 6 x 5 = 30%

Instinct Not Stated 30%

Regeneration: 3 rounds after being damaged, start regaining 1 Wound/3hp per round. Severed limbs reattach.

Return from death: If killed (0 Wounds), will regenerate and fight again in 1d10 rounds.

Fire and acid: Cannot regenerate damage from these sources. The only way to permanently kill a troll.

Instinct [-] or flee when attacked with fire or acid.

 

Hull Breach Conversion Document

TROLL

AP 5

2 Wounds

Health 30

Attacks 2 × talon (1d10), 1 × bite (2d10)

[12+10 = 22 as 1d10s is 2d10 split between 3 Attacks, with arbitrary +1d10]

Combat 30%

Instinct 20%

Regeneration: 3 rounds after being damaged, start regaining 3hp per round. Severed limbs reattach.

Return from death: If killed (0 Wounds), will regenerate and fight again in 1d10 rounds.

Fire and acid: Cannot regenerate damage from these sources. The only way to permanently kill a troll.

Fear of fire: Roll Instinct [-] or flee when attacked with fire or acid.

 

My Version

RED DRAGON

3 Wounds

Health 20

Combat 65%

Instinct 75%

10 AP

Attacks 2x claws (2d10) and 1 x bite (2 Wound) or breath 90'/30m cone of fire (2 Wounds + 1d10 damage)

Moves 1/4 slower than a human but flies twice as fast

Language and spells: 50% to know some form of reality warping spell; 3 × 1st level, 3 × 2nd level, 3 × 3rd level.

Found Sleeping: 10%

 

 

HUNDREDS

RED DRAGON

14 AP

11 Wounds

Attacks [2 × claw (2d10), 1 × bite (1 Wound + 2d10)] or breath 90'/30m cone of fire (11d10 Damage)

Combat 55%

Instinct 55%

Moves 1/4 slower than a human but flies twice as fast

Language and spells: 50% to know some form of reality warping spell; 3 × 1st level, 3 × 2nd level, 3 × 3rd level.

Found Sleeping: 10%

 

Hull Breach Conversion Document

RED DRAGON

3 Wounds

30 Health

Combat 40%

Instinct 30% (1 x 20 + arbitary 10)

AP 6

Attacks 2 × claw (1d10), 1 × bite (3d10) or breath (5d10 Damage)

[6d8/45 is 48/45, is 5d10 each]

Moves 1/4 slower than a human but flies twice as fast

Language and spells: 50% to know some form of reality warping spell; 3 × 1st level, 3 × 2nd level, 3 × 3rd level.

Found Sleeping: 10%


What is clear here is that all conversions are very bad at handling small HD creatures. I think that's a reflection of Mothership focusing on the Alien single-monster rather than 3d10 Space Orcs in a room. As expected for a professional product, the Stars Without Number adaption was probably the most consistant at 3 HD or higher, but has the issue that it was made for characters rather than monsters.
I think my version could learn something from both.

I've been reducing the number of Wounds and Health far too much as they climb. And I forget in D&D that 1 HD is pretty tough compared to a Normal Human who has 1/2 a HD or 1d6 HP depending on the edition.

The changes I would make

HD = Wounds

HP = Health, if HP is under 10, add +1d5+6 (Allowing 1 HD monsters to have between 11-15 Health), add the OSE HD modifier to Health if average not listed.

At the Warden's discretion, really small animals can just keep the HP as Health for being fragile.

If 4 Wounds or higher, halve the Wounds and the Health

If this reduces the new Health total to 10 or less, add 10 to the Health. and round up to the nearest 10.
If the Warden does not like the high Wound and low Health end result, they can halve the Wounds again and double the Health.

Add 1 Wound as a bonus.


Orc Chieftain: 4 HD/15 HP, Becomes 2 Wounds 7 Health, add 1/10 and round up for a final 3 Wounds and 20 Health or 1 Wound and 40 Health

Troll 6 HD/30 HP, Becomes 3 Wounds 15 Health, Which becomes 4 Wounds and 15 Health or 2 Wounds and 30 Health

Red Dragon 10 HD/45 HP, Becomes 5 Wounds 22 Health, which becomes 6 Wounds 22 Health or 3 Wounds and 44 Health


Hey you know what the second results look like?

The Hull Breach Conversion where it's HD/3
But the Goblin in, There is a Goblin on Icarus Station is 10(15) Wounds(Health).
So they may be about the same as the original idea of high wounds and mid-range health.

But certainly at low HD (under 3 HD) under the SWN Conversion Guide, it would be wise to just bump up the Wound by 1 if the monster is supposed to be fought. Knock off Health down to 10 if so.

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