Berries have been a part of the Pokemon universe since Pokemon Gold/Silver where they could be held by a Pokemon in battle. Generation 3 and Generation 4 added more berries as well as the Poke Block/Poffin gameplay mechanic. Pokemon Legends: Arceus takes place in ancient Sinnoh, meaning there isn't a way to use berries to cook Poffins like in Diamond/Pearl/Platinum and the remakes. Instead, berries are used to craft throwable items that can be used to distract wild Pokemon, or they can be used in their plain, natural form.
Aguav Berries were introduced back in Generation 3. They were a holdable item that would restore a quarter of a Pokemon's health, but only if the Pokemon's HP dropped below half. If a Pokemon had a Rash, Lax, Naughty, or Naive Nature, then the Pokemon would also get confused upon consuming it. Confusion doesn't seem to exist in Pokemon Legends: Arceus, but a Pokemon with the correct Nature will pause after it's eaten one. However, with the Daybreak Update, it may be wise to keep any Aguav Berry in storage.
Pokemon Legends: Arceus — How to Get Munchlax and Evolve it into Snorlax
After completing the main story, players can then start a series of Requests involving massive mass outbreaks of Pokemon. Speak to Warden Mai in the Obsidian Fieldlands to start the Request: A New Anomaly. Bear in mind that Legends: Arceus needs to be updated to V.1.1.0 for this to occur.
Once players are ordered to investigate massive mass outbreaks in the Crimson Mirelands, they'll run into Melli, who will hand over 20 Aguav Berries. Unfortunately, Mai's Munchlax will consume five of them, but it turns out Munchlax has an odd ability that lets it identify all the Pokemon in massive mass outbreaks. This means players can simply
Read more on gamerant.com