Ever since first edition Gamma World I’ve been fond of this “monster” because it embodies the setting’s ethos of “even the landscape is out to get you”. I’ve updated it for the current edition of the game, with a little added benefit/story hook to encourage characters to actually brave the risks involved, making it a bit more than just a random hazard.
Gamma Grass: Known as “zeeth” in the language of the seer lizards, this purple sward reproduces by teleporting its seeds into the guts of nearby creatures. The seeds release a deadly neurotoxin, killing the host, which decomposes and fertilizes a new patch of gamma grass.
Mature gamma grass is a hazard that attacks any animal creature that begins or ends its turn within 5 squares of the patch. Seed teleports that miss materialize in the air nearby with a sizzling “pop” as they burst harmlessly.
Attack: Ranged 5, +7 vs. Fortitude. Targets protected by force fields are unaffected.
Hit: 2d6 poison damage, plus ongoing 5 (save ends). If target drops to 0 hit points or fewer, it dies and a patch of gamma grass sprouts from the corpse the next day.
If mature gamma grass is harvested, dried, and smoked, it grants a particular type of alpha shift: the smoker may draw the next two Psi mutations from the alpha mutation deck and choose to retain one, gaining a +2 bonus to overcharge that mutation for the next encounter.
Because of its benefits (along with a mild euphoric “high” from smoking it), serfs, sleeth, and some badder tribes use slave labor to harvest patches of gamma grass. Those that do not survive the process simply ensure a bumper crop in the following season.