A genetic engineer, Q, is a type of monster that originates in SLASH'EM, and also appears in SlashTHEM and xNetHack. Its sole melee attack is weak, but can polymorph any monster it hits unless the target has magic resistance or sufficient magic cancellation.
The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.
Genetic engineers now appear in NetHack 3.7. They can generate outside of Gehennom and are eligible to appear via the summon nasties monster spell. Genetic engineers will teleport away if possible after changing a monster with their polymorph attack; this includes you if you are polymorphed into a genetic engineer.
Eating a genetic engineer corpse will cause you to polymorph as a chameleon or doppelganger corpse does - this also applies to pets and other monsters, but pets will not eat poisonous corpses unless they have poison resistance, and additionally avoid corpses that would cause them to polymorph unless they are starving or on the verge of untaming.
If you are hit by the polymorph attack as a werecreature, it will switch you between your natural and beast forms.The current tile image is from SLASH'EM; vanilla uses a different tile (no glasses, holding a strand of DNA) which should probably replace it.
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"Write up info for other variants"
The genetic engineer is generally a dangerous opponent, since it can easily polymorph you into a form that breaks armor or else shrinks out of it - this in turn will usually leave you susceptible to being polymorphed further, since you will not have any magic cancellation. Fortunately, they are typically only encountered around Gehennom, and you should have a source of magic resistance before then. Players without magic resistance should use their best ranged attacks to kill off a genetic engineer before they can get into melee range.
Do not use conflict around genetic engineers if at all possible: monsters in SLASH'EM revert to their original form if killed while polymorphed, effectively giving them an "extra life". This causes fights to drag out longer than necessary even in best-case scenarios, and as with other instances of monsters polymorphing this may create highly-resistant monster forms such as the magic-resistant crystal golem. While the attack is subject to enchantment resistance against other monsters, this should not be relied upon for conflict-based strategies. Players seeking to use conflict should prioritize killing any genetic engineers nearby first.
As a polyform
The genetic engineer also represents an interesting strategy for players that use polyself often: their polymorph attack triggers whether or not you are fighting with bare hands in that form, and ignores magic resistance scores against monsters, allowing you to bypass or even tame numerous monsters that are either very formidable enemies (e.g. Archons and giant shoggoths) or very difficult to tame (e.g. Planetar and Solar). This also allows you to tame monsters for which taming is normally impossible - for example, this is the only way to tame Death in SLASH'EM that preserves his current form, as opposed to sliming him and taming the resulting green slime.
Gray dragons and other monsters with player-style magic resistance are completely immune, while monsters with armor that provides magic cancellation can prevent your attack from working immediately. Shopkeepers, aligned priests, and hostile minions can never be tamed, even if polymorphed. In addition, the effect is also subject to enchantment resistance, meaning that it will not work unless you are wielding a weapon of the appropriate enchantment to hit that monster with.
Otherwise, the genetic engineer form is not very strong; many monsters are capable of killing you and revert you to normal before you get a chance to polymorph them, particularly if you are surrounded. As noted above, there is also the ever-present risk of creating a stronger monster that you cannot defeat. Furthermore, hitting a monster and polymorphing it into a form with passive attacks will cause the new form's attacks to trigger rather than any the old monster - if you are trying to polymorph a monster, be sure to wear gloves to prevent YASD in case that monster becomes a cockatrice, asphynx, basilisk, or a similar monster.