The goal is to use Basic/Expert D&D and Gamma World together to create a pulp sci-fi space opera or sword and planet game.
A couple of approaches have already been presented in the first edition Dungeon Masters Guide for AD&D and Gamma World and also in Mutant Future for use with Labyrinth Lord.
These suggestions are just for those who would like to try something a little quicker.
Use mainly the rules for D&D. Use rules from Gamma World for mental attacks and technology.
Clerics = Cosmic Clerics
Dwarves = Aliens
Elves = Alien Warlocks
Fighters = Soldiers
Halflings = Aliens
Magic Users = Stellar Sorcerers
Mutants (Animal or Human) = Aliens, cyborgs, mutants
Thieves = Scoundrels, rogues, whatever you want to call them
Starting HP = CON.
At second level and above, D&D characters roll hit points per class and Mutants roll 1d6 for hit points.
D&D characters roll per class. Mutants roll as Thieves.
All characters use their WIS score as Mental Strength against Gamma World mental attacks.
Cleric Points = WIS
Magic Points = INT
Mutant Points (Physical Mutations) = CON
Psionic Points (Mental Mutations) = CHA
When using a spell, mutation or psionic player rolls 2d12.
If power throw <= current power points then the power works as written in rules.
If power throw > current power points then power does not work and subtract 1 point for new current power points total.
If current power points go below 8 then something bad happens (determined by DM) each time more power points are lost.
What could go wrong?
Power points heal 1d6 per 12 hours, not above starting power points.
Many modern or sci-fi rpg settings include long lists of skills to define the character.
In this game attribute rolls are used for skill use.
To keep it simple, the player picks three things the character is not good at.
For example: electronics, swimming, piloting
Skill roll is a d20. If roll <= attribute then skill succeeds.
The attribute roll for something the character is not good at is made at a -3.
D&D Magic Items = Technology with added energy limitations or ammo
Wands = pistols, rifles
Gamma World Items = Either stuff that could accidentally melt your face or blow up real good.
Think weird science Flash Gordon/Buck Rogers etc.
Of course it's up to the GM to decide how easy it is for characters to figure out how to use technology.
Sorry, nothing here yet. Import rules from your favorite game.
I think anyone who has made it this far can find a way to customize existing creatures or make up their own.
STAY TUNED FOR MORE ADVENTURE!