Necrozma Quest
The Necrozma Quest was added to PokéHeroes on July 1st, 2023, as part of the 10th Anniversary celebration.
Once activated, you will be asked to complete several tasks, ordered by three, and ends once you successfully beat Necrozma.
Intro
Once you enter the Ancient Cave and choose the Necrozma Quest, a new character, Keshi, will talk to you. They will try to play the Old Vinyl, which will fail, causing the Old Vinyl to shatter in several pieces. Getting those pieces will require you to complete several tasks across PokéHeroes.
First Three Tasks
The first three tasks involve the Royal Tunnel, the Berry Garden and Emera Beach. A task that is completed, will be struck-through to indicate you don't need to do it anymore.
The Vinyl Piece for the Royal Tunnel randomly shows up after correctly answering a question. It has the same format as a Gem being found, so it is possible to miss it. You don't need to click anywhere, it will automatically count as "completed".
You do not need to complete the Tunnel, so you can attempt this in the Endless Path.
When entering the Berry Garden the first time after activating the Quest, Lorelei will show up and mention a weird seed, the Dark Seed. You will be tasked with growing 100 of those Berries, to help Lorelei study them.
You can have Berries of several levels, as long as you total is 100 or higher. You might have to refresh the Garden-page, as harvesting Berries does not do that automatically.
If the message doesn't show up, reload the page.
Visiting the Beach after activating the Quest, will show a dark sky, regardless of the time of day.
Leah will be talking to you about the darkness and ask you to catch a Fish Pokémon that glows. Possible Pokémon are : Inkay, Chinchou, Lanturn, Finneon, Lumineon.
Tynamo will NOT work, because the PokéDex mentions needing many to get some light.
A shiny pokémon will also work, with a slightly different message.
You cannot do any trades with Leah, as it will be too dark for her to see the fish/items you're trying to trade.
Next Three Tasks
After finding the first three Old Vinyl Pieces, Keshi will give you three more tasks to find the remaining three pieces. These tasks will involve the Shadow Radar, interacting and the Lab.