Lockseon by @Eternity9

Type: Grass / Fairy

Ability: Keen Eye

Hidden Ability: Infiltrator

Classification: Outlaw Fakémon

Dex Entry:

             Lockseon is a rare Fakemon that is said to have been the companion Pokemon to a heroic outlaw from many centuries ago, though it is believe to be just a legend. The Legend also says that you can only obtain this rare Eeveelution if you are able to find the forest where a special Rowlet's and its Evolution line can be found roaming free and if you do find the forest you must find a clearing with a tree stump with a strange arrow stuck in its center ring....from their the text becomes unreadable. 

Game mechanic wise I would have this be an event, where the player character can come across a mysterious piece of parchment on the ground, on what even route they happen to be in when starting the event, this parchment will have a riddle inside, which the player has to figure out to find the hidden location. After figuring out the riddle (Or look online for help) the Player Character will be allowed accesses to a 'hidden grotto' though in this case its a 'Hidden Forest' where they will encounter Rowlet's and some 'special' Rowlet's with a unique colour pallet, but they aren't shiny. Eventually the trainer character after getting past the forest maze will come across a tree stump in the middle of an opening in the trees. When the player character steps over to the stump, suddenly a arrow will shoot out from nowhere and stick into the center of the stump and then suddenly an ancient Decidueye (Totem Pokemon) will make itself known and the player character must defeat it if they want to obtain the item 'Outlaw's Arrow' that will evolve eevee into Lockseon.