I mean obviously triffids should be D&D monsters. There are various ways you can adapt this, because Wyndhams work has been adapted for film and television many times. But this version is reasonably close to the original.
Triffid
by Cab Davidson
| Stat | Triffid |
| AC: | 7 |
| HD: | 5* |
| Movement: | 60’(20’) |
| Attacks: | 1 stinger |
| Damage: | 1d6+poison |
| Number Appearing: | 1d6 (5d20) |
| Save As: | F2 |
| Morale: | 12 |
| Treasure Type: | V |
| Intelligence: | 0 |
| Alignment: | Neutral |
| XP Value: | 350 |
The triffid is large (7’ to 10’ tall and around 4’ across) plant like monster, with a large, muscular set of roots that it can use to pull itself up from the earth and drag itself along the ground. They start as tiny seedlings, needing sunlight and water to grow, but as they approach adulthood they uproot themselves and head towards animal prey.
The upper part of their body is reminiscent of a giant pitcher plant, shaking as the lower part of the plant drags it along the ground. Smaller branches beat on the trunk as it moves, giving it a characteristic clicking sound (of unknown purpose). It will travel towards any animal prey within 120’, and when within 10’ it can strike with a stinger encased within its pitcher. The stinger inflicts 1d6 damage, with a save for poison being necessary to avoid instant death. After it has killed, the triffid roots itself nearby and feeds upon its victim.
Triffids reproduce by releasing thousands of downy seeds from seed pods near the top of their pitchers. Most are infertile, but sufficient do germinate to mean that they can reach plague levels very quickly.
While young triffids are plants requiring sunlight, earth and water to grow, as they mature they can follow prey into caves, where after feeding they may remain dormant for years, remaining dangerous to any passing creatures.