Editing Gamma World (section)

==System==
Throughout the game's many editions, ''Gamma World'' has almost always remained strongly compatible with the then-current edition of ''[[Dungeons & Dragons]]'' (''D&D''). Attribute generation is much the same for instance with a range of 3 to 18, randomly generated by rolling three six-sided dice. The attributes themselves are the same, but with occasional name changes such as Physical Strength instead of Strength and Mental Strength instead of Wisdom. This allows Gamma World and D&D characters to potentially cross over genres.

Character generation is mostly random, and features one of the game's most distinctive mechanics, the mutation tables.  Players who choose to play mutants roll [[dice]] to randomly determine their characters' mutations.  All versions of ''Gamma World'' eschew a realistic portrayal of genetic [[mutation]] to one degree or another, instead giving characters fantastic abilities like psychic powers, laser beams, force fields, life draining and others. Other mutations are extensions or extremes of naturally existing features transposed from different species, such as electrical generation, infravision, quills, extra limbs, dual brains, carapaces, gills, etc.  These were offset with defects that also ranged from the fantastical—such as skin that dissolves in water, or a scent that attracts monsters—to the mundane, such as seizures, madness and phobias.

Characters in most versions of ''Gamma World'' earn [[experience points]] during their adventures, which cause the character's Rank (in some editions, Level) to increase.  Unlike ''D&D'', however, the first two editions of ''Gamma World'' do not use a concept of true level or [[character class]], and increases in Rank do not affect the character's skills or combat abilities.  In fact, in the first three editions of the game, character rank is primarily a measure of the character's social prestige.

The [[game mechanics]] used for resolving character actions, on the other hand, greatly varied between ''Gamma World'' editions. The first two editions, like the early editions of ''D&D'', depend heavily on matrix-based mechanics, where two factors (one representing the actor or attacker, and one representing the opponent) are cross-referenced on a chart.  For some actions, such as attacks, the number located on the matrix represents a number the acting player must roll.  For other actions (such as determining the result of radiation exposure), the matrix result indicates a non-negotiable result.  ''Gamma'' World's first two editions had a variety of specialized matrices for different situations (again, closely resembling ''D&D'').

The third edition rules replace specialized matrices with the Action Control Table (ACT), a single, color-coded chart that allowed players to determine whether a character action succeeded, and the degree of success, with a single roll.  (The ACT concept is drawn from the ''[[Marvel Super Heroes (role-playing game)|Marvel Super Heroes]]'' game published by TSR shortly before development of ''Gamma World''<nowiki>'</nowiki>s third edition.)  The ACT requires the referee to cross-reference the difficulty of a character action with the ability score used to complete that action, determining which column of the ACT is used for that action.  The character's player then rolls [[percentile dice]]; the result is compared to appropriate column, determining a degree of success or failure and eliminating the need for second result roll (e.g. the damage roll that many games require after a successful combat action).

The fourth edition was directly compatible with 2nd Edition AD&D with some minor differences in mechanics. The fifth and sixth editions though would relegate Gamma World to that of a Campaign Setting and require the core books to play. 5th uses the Alternity system which is mostly represented in the book but required the core rules in order to resolve some factors. 6th Edition though was fully incomplete on its own and required the d20 Modern rulebook in order to play the game.

The seventh version uses a streamlined version of ''[[Dungeons & Dragons 4th edition|D&D 4th edition]]'' mechanics. Character generation choice though was nearly fully removed. Instead of choosing a character class, a player had to roll a twenty-sided die two times and consult an accompanying character origin table. For example, a player might obtain the result "Radioactive Yeti" and gain the powers associated with the "Radioactive" and "Yeti" origins. Attributes, mutations, and skills were also randomly assigned. Two decks of cards comprising the core of a ''[[Collectible Card Game]]'' are included with the game. One deck represented random Alpha Mutations, which could be drawn to gain temporary powers, and the other contained various Omega Tech, powerful technological devices that could possibly backfire on those that used them. Some 4th edition rules enhancements for the setting include new damage types such as "Radiation", Gamma World-specific skills, and increased lethality. Despite these differences, it is possible to use characters and monsters from a ''D&D'' game in ''Gamma World'' and vice versa.