mutator

What it means

1. That which causes mutation or change.

   In object-oriented programming, the mutator function changes the value of the field that gives its name.

2. video gamesA setting which alters specific gameplay mechanics, such as rules, physics, or abilities.

   Rocket League will gain match-modifying mutators […] The football-meets-cars mashup will let you toggle on gameplay-changing settings such as low gravity, time warping and explosions.

   2015 October 28, Tom Phillips, “Rocket League match mutators to arrive in free November update”, in Eurogamer.net

In a sentence

In object-oriented programming, the mutator function changes the value of the field that gives its name.

Where it comes from

From mutate + -or. The video gaming sense likely originated in the video game Unreal Tournament (1999).