The Mothbug is the companion that accompanies you through the valley, and it is worth understanding what it actually does rather than treating it as an accessory. It assists in both traversal and combat, which makes it a second set of verbs rather than a follower.
The useful framing for the Mothbug is that it extends your options in a space rather than reacting to you. In traversal it provides assistance in places where your own movement kit has gaps. In combat it contributes in ways that shift the rhythm of an encounter. If you treat it as decoration, you will underuse it and miss part of how the game wants fights to feel.
There is a Sanctuary hub where residents and meals feature, and it functions as the game's rest point and social space. For a game built around a large valley and escalating boss encounters, a hub with people in it is a meaningful anchor - it gives the journey a place to return to and a reason to keep going, and it is where the rest of the cast of Viridia lives.
A traversal system built on chaining moves tends to leave a player who has learned the chain very little else to do in a tough spot. The Mothbug is what keeps options open when the chain does not work, and in a game with large boss fights where positioning matters, that backup is what keeps a run from ending on a single mistake.