Walkthrough Guide:
1. Obtain a Shadow trap
Adventure: Obtain a Shadow trap
In this place, you have to equip your best Shadow trap to catch the mice here.
If you do not have any Shadow trap yet, you can buy the Ambrosial Portal Trap or Sinister Portal Trap for 8,000 gold and 9,800 gold respectively from Mousoleum - Trapsmith.
Alternatively they are also available at the same price at the following stores:
In addition, if you want to support Mousehunt, you can also buy Creepy Coffin Trap from Mousoleum - Trapsmith. It is stronger Shadow trap than the 2 above. It costs only $1 and gives you Lucky Shield (Luck bonus) for 1 month.
But if you already have any better Shadow trap, use that instead of course.
Thank you to /u/aswifte@Reddit for letting me know about the price of the Shadow traps have been reduced starting from Halloween 2018
2. Brew Radioactive Blue Cheese using or Greater Radioactive Blue Potion
You do not need to convert all your Brie Cheese at once. It is recommended to convert with small amounts of potions.
As converting the cheese consumes gold, you do not have to convert all your Brie at once; just convert with 1 or 2 potions, and use the gold you will be earning to convert more. Also note that as you level up, your potions become more effective and can convert more cheese. This is another reason not to use all your potions at once.
3. Collect 30 Cemetery Slat to Build a Barricade
Adventure: Travel to the Mousoleum and Collect Cemetery Slats to Build a Barricade
Now that we have the setup ready, the hunt is on!
The next target is to collect the Cemetery Slat dropped by the mice.
Continue converting Brie Cheese into Radioactive Blue Cheese as needed.
4. Craft Crimson Cheese by gathering enough Crimson Curd from barricaded mice
Adventure: Craft Crimson Cheese and Capture Mousevina von Vermin
Larry says, "With the barricade up, you will now be able to explore the tombs where the more powerful ghostly, ghoulish and vampiric mice reside."
5. Use Crimson Cheese to attract and capture Mousevina von Vermin
Adventure: Craft Crimson Cheese and Capture Mousevina von Vermin
And finally is to catch the boss, which is Mousevina von Vermin.
Simply equip Crimson Cheese to do so, and once it is captured, your adventure in Mousoleum is pretty much done.
You will also get Shredded Furoma Map Piece for catching it. You can repair this to be Stitched Furoma Map Piece in Bazaar - Cartographer to access Furoma region once you hit Grandmaster.
Do not forget to claim the "Slay Mousevina von Vermin" Adventure to get bonus gold and points.
6. Preparation for next
If this is your first time clearing Mousoleum, then the next area to visit is Great Gnarled Tree.
But before you go, keep hunting here to collect Radioactive Blue Potion to brew at least 30 Radioactive Blue Cheese.
If you have cleared Great Gnarled Tree and this area, it is recommended to hunt in Great Gnarled Tree until you reach Grandmaster as the mice there drop Gnarled Potion required for next area, Lagoon.
For details, go to Great Gnarled Tree Guide.
Note that starting from Halloween 2018, this mouse no longer drops Shredded Furoma Map Piece.
Thank you "coolboy98#0785@Discord" for reminding me about Crescent Cheese