A reasonably well-kept path provides the party with mostly straightforward traversal through the thick jungle. However, dangerous creatures seeking their next meal wait to ambush unwary travelers, and a protector of the jungle lends them its magical aid.
This scenario works for a standard jungle, but it's especially appropriate for warm faery pocket realms or any sort of enchanted forest. The kirin is not a particularly malevolent creature, but it's quite territorial and protective of the jungle and its creatures from outside interlopers (while otherwise ignoring the natural food chain cycle). As such, the PCs aren't in much real danger for their lives; the kirin hopes to send them running out, hurt and warning others not to travel this way, and the dragonflies are unlikely to slay a third-level PC that has an escape route.
If the details are important, you could have the path be maintained by locals who have the kirin's blessing as being part of the jungle. Or, the kirin itself could maintain the path since it has some trouble maneuvering in the thick brush itself.
A line of path sections (-) winds through thick jungle brush (B), crossing a river (|) with the help of a wet, slippery log (X). The path and river sections are lit, but the brush sections are shadowy due to the thick canopy and plentiful foliage. Keep in mind not to reveal the enemies in the brush to the players at the start of the scenario.
The brush immediately near the path (that on the map) can be traversed, but it slows movement. All normal Moves (those other than flight, phasing, and teleportation) into or out of a brush section have a maximum distance of 1, and Strategy entries on mounts that provide movement, as well as the Kirin's Gallop, do not provide movement into or out of a brush section. Beyond the brush sections on the map, the jungle is too thick to pass through in combat time (though phasing into or flying over might be possibilities if the PCs have access to such).
River sections require swimming. The slippery log is hazardous to traverse without falling into the river. An entity that moves onto or attempts to move off of the log (except into the river) must succeed on an Acrobatics vs. 1d4; failure results in falling into the river (occupying the same section, but swimming in the water alongside the log instead). This same check must be attempted whenever an entity on the log suffers damage.
The Kirin, or any entity that either Moves 2 or uses a normal Move and a mount's Strategy Move together, can bypass the log by leaping over it (and the river) from one side of the path to the other. This does not require any check. This maneuver cannot be attempted into or out of a brush section; it must be from path section to path section (or the entity will fail and fall into the river).
Similarly, the Dragonflies may use their normal movement together with Soar to pass over any river section. They may do this without regard to brush.
Combat begins when the Kirin makes its presence known to the PCs, appearing on the path ahead and summoning its light magics. If the battle stretches toward the edges of the path pictured, extend the map following this general setup.
B B B B | B - B - - B | B - B B B - - X - B B B B B | B B B | B
The Kirin relies on hit-and-run attacks, pelting the PCs with Dancing Lights and healing damage suffered from ranged attacks (which it's most likely to draw, being in the open path). It will use Gallop to leap the log and run from mounted PCs, but otherwise it prefers to use Coat of Brilliance to punish ranged PCs.
The Dragonflies are less skittish and will move about in a more aggressive manner. They'll pelt PCs on the path with Spitfire, and they're not afraid of fighting in melee within the brush. A Dragonfly reduced to less than 10 HP will Soar to brush sections close to the Kirin to enable healing from Dancing Lights.
Additional enemies charge from the brush, surprising advancing PCs (5+ players). If charging PCs pass them by to reach the Kirin, they'll head toward ranged PCs or those that fled into the brush.
With the beasts defeated, the PCs are free to continue on their way. Heroic parties may spare the Kirin, which will respond to their mercy with like kindness.
The PCs are chased from this part of the jungle, suffering an Injury. The Kirin's restorative abilities means that any defeated Adversaries will be back and at full health if the PCs choose to return.
If you have five players and don't want to deal with the Triffid and Bolt Rat, you could simply use a third Dragonfly instead. Alternatively, if your jungle is in the mountains, consider a Lode Spider, though with its large lumbering body, it should give away its position even within shadowy brush.
At lower levels it's often appropriate to assign effects such as Miss bonuses against ranged attacks while within brush. By level 3, such mundane terrain details are no longer serious impediments to either the PCs or their Adversaries. Save effects like this for unusual or magical terrain from this point forward. If you want to include such effects in this scenario, add some plants with atypical properties, such as rock-hard fronds or trees with limbs that move about. This is more appropriate in something like a faery pocket realm or other enchanted forest.
The river here isn't much of a hazard, briefly imposing a couple penalties when a non-Aquatic entity occupies it. If you want to beef it up, make it river rapids studded with rocks; entities that fall into the river (but not enter willingly) or start their turns there are immediately pulled northward 1 section and suffer 2d4 damage from getting banged up on rocks. You may allow PCs with the Aquatic keyword to make challenging Acrobatics rolls (vs. 1d10 or 1d12) to avoid one or both effects. For extra danger, turn the entire north wall of the map into a cliff, with the river becoming a waterfall. Height 3 or so would be appropriate. This is unlikely to be an issue unless a PC acts incredibly foolishly, given that the Adversaries here don't engage in forced movement and the river can be crossed plenty south of any waterfall.