"Woodknot straightened his back, his brow damp from sweat from the sickness. He looked down at the rows of trees that once filled the cospe with beautiful leaves and fruit. His
evil work complete, the old druid smiled with malign pride. Browning leaves shifted in the wind showing clumps rotting fruit that had begun drop to the forrest floor in wet mushy heaps. A loud rythmic stomp shook the ground as the corrupted oakheart lumbered out to spread decay."
Its Bite is Worse than its Bark
The Corrupted Oakheart is a treant twisted by disease or decay. This monster could be infected by a naturally occurring pestilence or be the result of a malevolent outside force, such as an evil druid or fey. In my game the corrupting oakheart was created by a lich who needed to weaken the defenses of a powerful archdruid and his grove.
The lich was after a powerful item protected deep in the Druid’s demesne to reach his goal the undead mage began corrupting the flora, bending them to its side creating an army capable of bypassing the groves wards.
Other Corrupted Oakhearts are grown from seedlings rather than corrupted as fully grown treants. These plant creatures normally spring up in biomes suffering from pollution or dark magic. Swamps or forests inhabited by powerful evil dragons are the ideal propagating grounds for corrupted treants. The domains of black dragons make a great setting for Corrupted Oakhearts.
The abilities of the new treant stay true to the base stat block. But to add flavor I wanted to give the monster a new ability that would make it more thematic. The Retch Swarm ability helps to add to the theme while also giving the oakheart multiple allies on the battlefield.
Adding flavor isn't always about adding more damage per round in combat. The new feature of the Corrupting Animation ability helps to give more depth to the monster and help add elements for storytelling in the hands of a clever Game Master.
Planting Corrupted Oakhearts in your Dungeons and Dragons Campaign
Any campaign centered around a nature based BBEG could use one of these plant creatures as a mini-boss or seige monster. Here are 3 ways to use a Corrupted Oakheart in your game.
The Corrupted Oakheart is a mini-boss standing between your party and their goal. In this instance the Oakheart gains Lair Action which I'll list below.
Use the treant as a guide for the party before the corruption has set in. Maybe the PCs have come to the wise treant for guidance. Use foreshadowing here so the group isn't completely taken by surprise later on. Using details like the treant's leaves are dull and wilting, its bark is peeling off or there is an abundance of pest crawling through the plant creatures branches.
Treants have the Siege Monster ability. This trait isn't lost after the creature becomes corrupted. If the party feels safe behind stone walls use this monster to shatter their sense of security.
Adding Lair Actions
If you want to use the Corrupted Oakheart as a boss we need to give it Lair Actions to make it more formidable. Taking inspiration from a boss battle from one of my favorite video games I came up with these three abilities: Sludge Bomb, Grasping Vine and Root Slam
Sludge Bomb targets a random enemy at range. The target makes a DC 15 dex saving throw. On a failure the target takes 4d10 acid damage as 1d4 oozes are retched through the air. These oozes have AC: 10, +5 to hit, deal 2d4 acid damage and can move up to 15 feet. They are meant to divide the players action economy rather than offer a real threat. If you want to up the danger exchange these oozes with more substantial ones from the Monster Manual.
Grasping Vines attempt to grapple a random player within 30 feet. This ability then reels the target into melee and engulfs them dealing 3d6 bludgeoning damage. DC: 15 strength save to escape the grapple. Each round an enemy is engulfed grants the Corrupted Oakheart 10 temporary hit points. Use the same To Hit modifiers as the Oakheart's Slam attack.
Root Slam lashes out at enemies within a 10 foot cone dealing 2d12 bludgeoning damage. If this ability hits, the targets must make a DC 15 strength or dexterity saving throw or be knocked prone. On a success the target takes half damage and is not knocked prone.
Sludge Bomb must recharge on a d6 but both Grasping Vines and Root Slam can be used at the beginning of each round.
Branching Out
I love plant monsters in TTRPG like Dungeons and Dragons and have a few other posts, one turning a dryad into a battlefield skirmisher. I hope if you're looking for something to spice up your nature themed encounters that the Corrupted Oakheart helps add a new challenge to your encounters and keep it interesting for you and your players.
If you like this twist on the D&D 5e treant how would you use it in your campaign? What kind of encounter would you build around it? Tell me in the comments. You can also follow me on Threads where I'm the most active at @LairActionsdm