Ekimmara Decoction
Effect: Damage dealt to foes regenerates Vitality.
Toxicity: 80
Duration: 30 minutes
Alcohol Used to Refill: ?
Location: ??
Ingredients
1x Dwarven Spirit
1x Ekimmara Mutagen
1x White Myrtle Petals
1x Mandrake Root
에키마라 : 노비그라드 트리스 메인퀘스트 / 벨렌 바이웨이즈 서브퀘스트
노비그라드 - [실마리를 따라서] 퀘스트에서 에키마라를 잡고 탕약을 만들려고 하니 변이인자를 못 얻었더라구요.
1회차때 탕약을 잘 몰라서 거의 엔딩 직전에만 몇개 써봤었는데요.
이제 뉴겜으로 난이도 높여 처음부터 다시 시작하니 보스몹들은 소재 줄 때까지 리트라이를 하게 되네요.
계속 되는 리트라이에도 변함없이 변이인자 대신 가죽만 나오길래.. 실마리를 따라서 퀘스트는 소재 고정인가 보다..하고 포기하려는 찰라 가죽이 아닌 귀, 피... 뭐 이런 것들이 나오는 것을 확인!
정확히 12번의 리트라이 끝에 에키마라 변이인자를 얻어서 탕약 제조 성공했습니다^^
Following the Thread

You will see this job on the notice board in Novigrad (M6,4). Go near the Southern gate. A guard is standing in front of the questgiver's house - he will answer your questions and direct you to nearby shed so that you can investigate the trail: blood, body and monster marks.

Follow the trail until you reach the river. Swim through it and enter the mill - there you will find an Ekimmara (level 11) and your colleague - Lambert. After eliminating the beast together go take the reward. Don't pick the option to move immediately -Ekkimara's skin is a valuable alchemy ingredient, it is better to take it now and join the other witcher later.
After a short conversation with the questgiver you will have to take care of three guards (level 11). Then, after a cutscene, go to the inn on the south. The dialogue options won't impact the outcome.
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Archgriffin Decoction
Effect: If any Stamina is available, strong strikes consume all of it
and reduce the struck foe’s Vitality by 10% after their normal damage is calculated.
Toxicity: 80
Duration: 30 minutes
Alcohol Used to Refill: ?
Location: ??
Ingredients
1x Dwarven Spirit
1x Archgriffin Mutagen
1x Ribleaf
1x Blowball
아크그리핀 : 옥센푸르트 숲에사는동물 서브퀘스트 / 벨렌 갑옷장인 서브퀘스트
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Troll Decoction
Effect: Regenerates Vitality during and outside of combat.
Toxicity: 80
Duration: 30 minutes
Alcohol Used to Refill: ?
Location: ??
Can be bought from the herbalist in White Orchard
Ingredients
1x Dwarven Spirit
1x Troll Claw
1x Crow's Eye
1x Honeysuckle
트롤 : 옥센푸르트 트롤부탁 서브퀘스트에서 트롤을 살려주지 않음 / 스켈리게 사라진광부 서브퀘스트에서 트롤을 살려주지 않음
Cave troll liver can't be farmed by farmable mobs as far as I know.
You will encounter 3 when you head back to Kaer Morhen as part of the main questline.
You can encounter another 3 during the followup quest to A Deadly Plot which is given after you help Triss escape Novigrad.
That cave is on Skellige, and is the location of the Enhanced Ursine Boots
in a sidequest for Djikstra involving the search for a certain shoe cobbler
I compiled what information I could on Ekimmara Hides and which recipes require them.
Enhanced & Superior Cursed Oil, Enhanced & Superior Elementa Oil, Enhanced & Superior Hanged Man's Oil,
So thats 6 total Ekimmara Hides.
From everything I've read you can get 3 total in the game.
Dragonslayer Grotto,
Contract: Mystery at Bywater,
Quest: Following the Tread
There might be a 4th during the quest Carnal Sins, depending how you do the quest you end up fighting a High Vampire that I believe turns into an Ekimmara. Not sure if he drops a hide or not.
So with that said you will be 2-3 Hides short of making all the oils that require it. So as of right now the only way to get all 6 hides would be through console commands on a PC version of the game and that requires you to get the debug console mod from Nexus. If you do use the console commands then the item you want to add will be Ekimma Epidermis. exact command: additem('Ekimma epidermis')
The name of the quest is "Following the Thread". You track and kill an Ekimarra in a water mill outside Novigrad. You aren't able to loot the body during the mission (I wasn't at least) because of a cutscene, but when you go back you should be able to get 1 hide and some other stuff off it. I'm playing on PS4 though, dunno if drops are any different there.
The mill is smack between the Sourthern Gate and Arette fast travel markers.