The lovely manga Delicious in Dungeon features the monster I'm about to detail, and while your PCs can cook and eat a dryad flower after defeating it, just like the characters in the manga, they don't have to.
Dryad flowers look like beautiful, naked humanoids of a variety of genders (including unusual varieties; they aren't picky), though their "skin" is usually a shade of blue or green. These "genders" are purely for show, however. A colony of dryad flowers (usually numbering half a dozen) are all tied to one central dryad flower, a "female," while the rest are "male." When the colony reaches maturity, the "male" flowers kiss the "female" flower, fertilizing it. The "males" then shrivel up and die while the "female" grows strange lumps, creating a grotesque tableau for those unlucky enough to stumble upon a colony at this stage. The lumps bud into actual flowers, and after sufficient flowering the "female" swells and explodes, scattering the flowers. These contain seeds which remain dormant for several years, begin passed on by birds and nature, before sprouting into new colonies of dryad flowers.
Male dryad flowers have two singular attributes. For one, within seconds they can form their body into a variety of shapes, still maintaining a basically humanoid contour while allowing them to, for example, form an arm into a tentacle or create webbing on their toes. This allows them to exist in and adapt to a variety of environments.
Secondly, when a male dryad flower is subjected to slashing, piercing, or explosive force, it explodes in a cloud of intense magical pollen. This quickly fills the lungs of all creatures nearby, causing what amounts to an instant, strong allergic reaction, making them much more vulnerable to the remaining dryad flowers.
For stats, I'm going to use the basic stats of the adult oblex. An ooze with a Challenge Rating of 5 is easy to imagine as a plant, and that CR can easily be shifted up or down a few levels by adjusting AC, attack, and damage.
We'll keep its amorphous and aversion to fire abilities, and convert its charm spell into a charm-like ability. We'll drop the rest of the spells, its sulfrous impersonation ability, and its eat memories ability, adding a poisonous pollen ability. The basic attack makes sense, changing its extra psychic damage to poison damage.
However, our dryad flower ends this transformation significantly weaker than an adult oblex. So, let's keep the multiattack but make that two regular attacks. That should keep up the pressure on the party.
OK, let's do this!
Homebrewery stat block:
medium plant, chaotic evil
- Armor Class 14
- Hit Points 75 (10d8 + 30)
- Speed 20 ft.
STR DEX CON INT WIS CHA 8 (-1) 19 (+4) 16 (+3) 14 (+2) 12 (+1) 15 (+2)
- Skills Deception +5, Perception +4
- Condition Immunities Blinded, Charmed, Deafened
- Senses Blindsight 20 ft., Passive Perception 14
- Senses Passive Perception 12
- Languages none
- Challenge 5 (1,800 XP)
Amorphous. The dryad flower can move through a space as narrow as 1 inch wide without squeezing.
Aversion to Fire. If the dryad flower takes fire damage, it has disadvantage on attack rolls and ability checks until the end of its next turn.
Charming Presence. When a creature sees a dryad flower, that creature must makes a DC 13 Wisdom save or be charmed by the dryad flower. The creature is immune to this effect until it finishes a long rest.
Poisonous Pollen. When a dryad flower is reduced to 0 hit points, it explodes in a cloud of pollen. All creatures within 10 feet must make a DC 13 Dexterity save. Creatures who fail their saves take the blinded condition and suffer one level of exhaustion, and can repeat the save at the end of every round.
Multiattack. The dryad flower makes two attacks.
Appendage. +7 to hit, reach 5 ft., one target. Hit: 7 (1d6+4) piercing damage plus 5 (2d4) poison damage.