Kallista remains in the cart, stabbing her sword down into the creature's "head."

Attack: 21 Damage: 4

The plant's head splits in several places. Though it seems weakened and oozes sappy blood all over the carriage and the adjacent road, it still keeps its grip on the wheels and stays standing.

Tender,` startled by the plant thing's appearance, manages to rally herself, using the carriage as a jumping-off point to aim a kick at the plant's center. After, she uses her momentum, pulling from the well of energy inside of her, to rain a flurry of blows down on the thing. 

Attack: 8 Damage: 6

Flurry of blows

Attack: 8 Damage: 6

Attack: 5 Damage: 5

(wow)

 Archer reaches for the plant but it pulls back before he can firmly grasp it and affect it with his spell, and Tender is too eager to strike the beast that her attacks miss.

Seeing his newfound companions miss their attacks, Orimdal jumps up and tries to position himself to cast Burning Hands, trying to ensure that his allies and the cart are not within the 15ft arc (Dex Save DC 12 or 11 fire damage).

(Wild Magic Surge: 13)

Dex Save: 20

(Totally forgot it was my turn there for a second. Sorry folks.)

The Plantopus lashes out at Fletcher with one of its tendrils.

Attack: 21 damage 9

Also if it hits you are grappled and restrained.

Fletcher tries and fails to dodge out the way of the grapple, however, raising his arm, he creates a shield of force that knocks away the tentacle (shield from Magic initiate, from variant human)

Evi, continuing to stay as far away from any foliage as possible, fires off another Eldritch blast at the plant monster.

Attack: 23 Damage: 10

(Includes +2  thunder damage from genie feature)

(completely missed the fact that it was my turn)

Fletcher, seeing the plant is focused on him, smiles. He intends to keep it that way. "OI! YOU OVERSIZED VENUS FLY TRAP!"

Running forward, Fletcher swings his enchanted sword at the creature Attack: 21 Damage: 12

Kallista wrenches her sword out of its head, whirls around, and stabs at it again from a different angle, using Fletcher's distraction to her advantage.

Attack: 11 Damage: 3 + 6 sneak attack damage (I'm assuming since Fletcher is making a melee attack that he's within 5 feet of the creature, but if not, disregard the extra damage)

(Well, actually, Fletcher managed to kill it with his attack, so you didn't need to attack)

Fletcher strikes one final, victorious blow to the beast, splitting its bulbous head straight in two. The creature lets out one last shriek, and its head explodes, spraying sappy blood over everything within several feet. Even the horses are slightly drenched in this sticky goo, and they begin to panic.

Edit: You all receive 200 XP for that encounter.

(Sorry Fletcher, I forgot that your shield spell was only your reaction to the previous turn)

After doing her best to avoid the spray of goo released by Fletcher's final strike, Evi moves back to the carriage.  Taking out her dagger, she'll move from wheel to wheel cutting off any of the remaining vines attached to them while also looking to see how much damage the carriage may have taken.

Investigation: 9

"Ew," Tender groans, looking down at where she's been covered in plant goo. Seeing the horses begin to panic, she scrambles to her feet -nearly tripping over her own tail- and goes to try to calm them down. 

"Easy," she tells them, putting her hands out, doing her best to project calm instead of the apprehension she feels. "It's alright, just a bit of plant goo; you're alright," she continues, all but cooing at the horses. 

(Animal handling, if needed: 22 )

Fletcher scratches his head. "Sorry guys, I could have been a little more careful with that"

Kallista wrinkles her nose, doing her best to wipe the goo off her face. "It's fine." Hopping out of the cart, she examines what's left of the monster, trying to figure out what it is.

(What type of check should I make to identify it?)

Orimdal flicks the goo off as he stands over the now dead creature. "Well this is a curious thing. I wonder what drove it ta us?" he says as he looks closely at the creature, trying to figure out how a plant could be animated and how it worked (Investigation: 3).

(I would say to identify the creature, make a Nature check)

Ormidal can tell that, although it is a plant, it seems to function like any other creature. It has a simple looking brain that allows it to perform basic actions, like hunting and devouring, and it has other organs that seem to function as stomachs, eight of them in total. Like other plants, it has veins that carry nutrients through its body to give it energy. At this junction, without further examination, it is impossible to tell whether or not it photosynthesizes or not.

The man at the front of the carriage wakes up suddenly, in a panic, as Tender tries to calm the horses. Panting and wide-eyed, he looks around, then calms when he sees the dead plant. "You killed it. Thank the Gods." He says. "It killed and ate the rest of my caravan. I escaped, but it must have followed me. I thought I would run down the road and warn any others I came across about it, and that's when I ran into you." He says. He tries to get up from the seat, but he is visibly weak. He quakes, and falls back down. "Ow." He says with a chuckle.

"There was just the one creature, right?" Kallista asks, hoping they won't have to fight off anything else.

Nature: 17

"I only saw one. It was so loud though, if there were any others, I'm sure we'd hear them." The man says.