⚔️ The Feline armor diagrams are in Novigrad.⚔️ It has a level 17 requirement.⚔️ You'll have to fight drowners, wraiths, a golem, and a witcher to get them.⚔️ The upgrade diagram locations come from buying Adalbert Kermith's maps at the Blackbough merchant, Crow's Perch quartermaster, and Lindenvale's armorer.
The Feline armor is a light set of witcher gear that turns you into a bit of glass cannon. It has less damage resistance, but it buffs attack power, and provides a passive where strong attacks buff fast attack damage, and you can "backstab" enemies, with rear attacks hitting harder and stunning opponents. The set has four armor pieces, two swords, and a crossbow.
You can get the Feline armor in a cave on the north side of Temple Isle (the northernmost island) in Novigrad. You'll also need Keira Metz's Eye of Nehaleni from her questline to dispel the illusory rock blocking the entrance. I show the route in the video above, but otherwise:
On the map, head to the northwesternmost house on Temple Isle and follow the path you can see snaking around it, down the trail into the cave.
Fight the golem inside now or later and then take a left through the tunnel to the room with the statues in a circle.
Pull the lever beside each as many times as necessary to make them all face inwards—this will open a pool in the centre with drowners.
The key you need is on a corpse at the bottom of the pool. I recommend saving first, and then diving as fast as you can to grab it, sticking close to the wall to limit the drowners hitting you.
Head back to the main room and use the key to unlock the door behind the golem.
Defeat Mad Kiyan, the crazed witcher in the room, and loot the armor diagrams from his corpse.
Read the laboratory log, also on Kiyan's body, and you'll get a marker for the location of the Feline Crossbow, which is in the Novigrad region as well.
Feline Crossbow
In the wreck of the Flying Stag ship on an island off the coast of west Novigrad, west of Drahim Castle and Lucian's Windmill.
Read Professor Sigismund Glogger's notes, also in the chest with the crossbow diagram to get the locations of the Feline Steel Sword and the Feline Silver Sword, again, both in the Novigrad region.
Feline Steel Sword
In Drahim Castle's basement just to the south of Novigrad's Glory Gate. Prepare to fight some bandits at the entrance.
Feline Silver Sword
In Est Tayiar to the northeast of Oxenfurt, east of the Vegelbud Residence. Destroy the wall to your right as you enter the ruin with Aard to find the diagram.
Once you've crafted the basic armor, you can upgrade it to enhanced, superior, and mastercrafted by finding the relevant diagrams.
Enhanced: Buy the Adalbert Kermith's first and second map from Blackbough's merchant to the west of Crow's Perch.
Superior: Buy Adalbert Kermith's third map from the Crow's Perch quartermaster.
Mastercrafted: Buy Adalbert Kermith's fourth map from Lindenvale's armorer, east of Crow's Nest.
🦅 Griffin: A medium set for signs🐻 Ursine: A heavy set for high defence🐺 Wolven: A medium all-rounder set
For grandmaster, when you head to Toussaint in the Blood and Wine DLC, speak to Lazare Lafargue in his armor shop in south Beauclair to start the 'Master Master Master Master!' quest to find the diagrams.