Initiative: 10 

Initiative: 3

The order is:

Ondrej

Evil plant 2

Genken

Lar-Dun

Evil plant 4

Arisys

Evil plant 1

Summer

Evil plant 3

(Assuming I'm within 30 ft of the closest plant:)

Ondrej lets out a howling laugh that grows into a battle cry as he rushes forward to meet the enemy. Holding his greatsword low to one side, he raises it up as he approaches the nearest plant creature, bringing it down in an overhead slice.

Bonus action: Rage

Greatsword Attack: 24 Damage: 15

The sword slices Evil Plant 3 clean in half.

Evil Plant 2 runs up to Ondrej and slashes at him with its claws, seemingly trying to avenge its fallen comrade.

Attack: 6 Damage: 4

Unfortunately for it, but fortunately for Ondrej, the attack bounces right off.

Genken bares his teeth at the oncoming plants, disturbing his restful travels and such. Not one to get his hands overly dirty, he maneuvers into a position to give himself distance from the attacking plants and nocks an arrow. He takes a breath and draws the string, aiming at the plant attacking Ondrej before loosing the arrow.

Shortbow Attack: 23 Damage: 4

Sneak Attack on hit: 4

The arrow flies past it, landing somewhere in the bushes.

Lar-Dun focuses his mind, extending a wave of fire from his hands, aiming it to get both plants in the cone but not his friends (Burning Hands)

Dex save from both plants.

Damage on fail (half damage on success): 9

Evil Plant 1: 3

Evil Plant 4: 17

Evil Plant 1 crumbles to the ground, reduced to a pile of smoldering coals.

Evil Plant 4, despite the fact that it's burning in several places, manages to stagger forward and swipe at Lar-Dun with its claws.

Attack: 13 Damage: 4

In a single motion, Arisys will draw her Boomerang and whip it towards the plant that attempted to strike Lar-dun. 

Attack: 12

If hit: Damage: 4  (The boomerang hits and falls to the ground)

If miss: The boomerang swings wide and arcs backaback towards Arisys, and she reaches up a hand to grab it.

The boomerang strikes Evil Plant 4 directly in the head, and it topples over, unmoving.

Her eyes glowing with arcane energy,  Summer draws her rapier which ripples with magical energy in the form of green fire circling the blade. Closing in on the plant Ordej is engaged with, she maneuvers herself into a flanking position and attacks on the other side.

Green Flame Blade (assuming I have advantage via flanking): Attack: 8

Damage: 10 

If Plant 4 is within range: 3 damage

The rapier stabs Evil Plant 2 through the torso, but when you pull it back, the plant is still standing and angry.

Green flames engulf Evil Plant 4's already-dead form.

(Question - I've been looking at the spell description for Green Flame Blade, but I think my brain isn't working and I can't figure this out. Does the first target take fire or piercing damage?)

(When casting the spell, it's treated as fire damage. If I perform Booming Blade, it becomes thunder damage.)

(Correct me if I'm wrong- I don't own SCAG so I'm going off a 3rd party app- but I think the first target just takes the normal melee attack and the fire damage is for the second target, until the damage scales at lv5.)

(Will we be using flanking? It might get complicated not having battlemaps doing totm.)

Ondrej wheels to face the last plant, sweeping his greatsword around in a horizontal swing.

Attack: 11 Damage: 14

The plant ducks under the sword, simultaneously clawing at Ondrej's legs.

Attack: 19 Damage: 2

(For the damage thing, I'm just going to go with fire for this instance because that's more damage to the plant and I'm feeling nice. As for flanking, that's true, it definitely could get complicated without battle maps. I'd say probably stray away from using it in the future.)

Genken repositions to ensure a clear shot at the plant attacking Ondrej. He draws the arrow in his bow and looses it at the creature.

Short bow Attack: 6 Damage: 5

Sneak Attack if hit: 4

(Yeah it's weird because on the character sheet the weapon damage for green flame and booming blade are listed as elemental. As for  avoiding flanking, I agree since we're doing theater of the mind.)

(Assuming the last Evil Plant isn't dead...)

Lar-Dun focuses his ire, concentrating it into a blast of fire.

Firebolt at Evil Plant 2: 18 damage: 4 fire

Once again, the plant just manages to dodge the arrow shot at it, but in its haste to escape, it fails to notice Lar-Dun's attack, and is completely incinerated.

An odd quiet falls over the camp. Two of the plants are reduced to glowing coals. The third has fallen apart into pieces and is slowly burning. The last has been completely bisected by Ondrej's sword, but is otherwise intact.