Once a verdant wood, this brown and gray forest is sickly, filled with shallow pools of acidic water and crawling with dangerous beasts. PCs passing through the forest, perhaps to find the cause and repair it, must first deal with some of its dangerous denizens.
The forest is shadowy regardless of the time of day thanks to the mossy canopy overhead. Trees and brush grant all entities +1 level to Miss dice against ranged attacks that lack the Area Attack property.
The + symbols indicate cliff borders of Height 2. These can be climbed with Acrobatics vs. 1d8, with each Move and successful check allowing for Height 1 traversal (so two Moves and rolls are needed to scale).
Sections labeled 2 and S are Height 2 above the rest of the battlefield. Section borders that lack a + have a slope that can be freely crossed to go from the base level to the higher ground.
Sections labeled with an A, as well as the one labeled Red, are pools of acidic water. In addition to requiring swimming, any entity without Acid Resistance that starts its turn in such a section suffers 1d6 Acid damage. Most Mounts will refuse to enter the pools.
Sections marked with a T have a large climbable tree at Height 1, scalable with Acrobatics vs. 1d4. As another Move, a PC that has climbed the tree can attempt to jump from a limb across one of the Height 2 borders to reach the cliff with Acrobatics vs. 1d6; failing results in a Height 1 fall. Similarly a PC can try to jump from the cliff to a tree limb with the same Acrobatics roll, but failing this results in a Height 2 fall. The Red Ooze can use Rapid Slide to scale a tree, but it cannot attempt the jump.
Note that these T sections can be occupied at the base of the tree and otherwise behave like normal sections.
The Wood Fiend cannot be discerned from a normal tree until it Moves, attacks a PC, or a PC enters its section. It is also revealed if it happens to get hit with an Area Attack.
It is presumed that paths continue through the woods at the west and east sides; draw these only if needed. The remainder of the map is surrounded by thickets too difficult to cross during battle (though if a PC has phasing you may need to deal with this).
Red 2 A T+ 2 A S T O + O O + PCs W O 2+ + O O S+ + A 2 2 T 2 O
The Red Ooze will advance and attack the nearest PCs. If it suffers from conditions or is out of useful cards, it will retreat to an acid pool.
Blasters will stay on the high ground, moving as needed to target anything within range. They will prioritize any PC that's trying to climb the cliff in order to knock them off, unless there's another PC already up the cliff advancing on them.
The Wood Fiend won't move until round 3, preferring to ambush the PCs as they move toward the eastern slopes that provide easier access to the cliff faces. If the PCs aren't interested in heading that way, it'll go ahead and attack sooner. If the PCs manage to wipe out all enemies before the Wood Fiend is revealed, end the scenario early. If there are five PCs, the Wood Fiend will probably only wait 1 round to see if a PC advances to engage the Triffid.
The PCs are able to continue through the forest to their destination. You could add a wounded traveler that the PCs have saved, who may have rewards or useful information, or put a corpse half submerged in an acid pool with 1 Wealth and a couple Valuables scroungable.
The PCs are forced to flee back the way they came, suffering an Injury. To avoid repeating the scenario, the PCs could choose a safer, perhaps longer, route around. Or, you could mix things up by changing the set of enemies and their starting positions.
Making the scenario dark instead of shadowy adds a sense of exploration to the forest and reduces the setup time. However, unless you indicate such with your descriptions of the area, the players won't know they can head east to access slopes to the higher ground, potentially ruining the Wood Fiend ambush. In this case you might shrink the battlefield by a couple columns and move the Wood Fiend closer to the PCs' starting position (directly adjacent instead of 2 away).
There are a number of other Adversaries that can work here. Take a look at the Thorn Shriek, Hobby Lantern, Mistling, Bolt Rat, Flamebelch Jeopard, Mindfang Spider, and Silk Spider to see if you want to use these to build your own set of Adversaries. You could also use a wide array of human adversaries to set up an ambush at this location, though such ambushers would need to rely on the PCs' own light to see to attack them.