The Odogaron and Legiana are two particularly annoying foes, but thankfully, nothing says you actually have to fight both at the same time. That’s not to say it won’t end up happening, as the Odogaron is an adventurous beast. You may see it up in AREA 12, where the Legiana likes to prowl, but the two are more likely to meet in AREA 8, which is where the Legiana will flee to after fighting for a bit… or where it’ll randomly fly if you neglect it long enough.

Focus on the Legiana first, and be sure to bring Flash Pods and Dung Pods. The former to help dispatch the Legiana when it’s being a little too… flighty, and the latter to discourage the Odogaron. Of course, you always could just let them fight, as your travels into the Rotten Vale have made it clear that they’re not natural friends. Endeavor to engage the Legiana in AREA 12, where you may find some hostile Gajalaka. While they’ll attack you if you bother them, they’ll mostly focus on the Legiana, especially if you keep the Legiana between yourself and the Gajalaka. If the Legiana gets put to sleep or paralyzed by the Gajalaka, it’ll be that much easier to kill it. Once the Legiana is dispatched, going after the Odogaron should be a relatively trivial matter.

After you’re victorious, return to Astera and talk to the Chief Botanist to get a view of the Ancient Tree in its ever-growing glory… which has now burst its bounds in another, curiously-timed growth spurt. After explaining matters, he’ll reveal your reward - the ability to cultivate three different materials at the same time! Score.