Get Coromon on Steam ➜ https://store.steampowered.com/app/1218210/Coromon/
My personal favorite way to gain milestone/research experience after completing most of the milestones such as brewing scents or naturalist. Located at the Battle Dome in Radiant Park which unlocks after beating the main story. Make sure to adjust your game settings for text speed, game speed, and battle speed in order to get thru dialogue very quickly. Start an easy trainer run and go as high as you can and just restart. With the changed settings this should move quickly getting your main milestone experience from battles won, researchers beaten, and fruits eaten. Happy farming! — Watch live at twitch.tv/derkradtv
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Make sure to check description for more information. Mainly just using system adjustments to greatly increase the speed of text and battles to do Battle Dome faster. Trainer Mode specifically for the researcher defeated milestone experience.