Source: Day of the Triffids
Location: All over the damn place
Threat Assessment: 3 going on 7. By it's lonesome a triffid isn't too bad. It's A large plant capable of movement with a long poisonous stinger. Trouble is, there isn't one triffid there are millions.
Limitation: Best weapon against the triffids was a type of crossbow device that shot out the equivalent of circular saw blades. If you don't have one of those a shot gun or flame thrower is fine.