There's a fireplace prior to entering the area with the Zeugl, but you're right, there's no fireplace in the area with it, so there's no opportunity to rest during the fight.As for which potions to use, firstly I'd probably stay away from using White Honey in the middle of the fight. If you want to reduce toxicity, there are other ways to go about it (as outlined by
ST_Ghost). Personally, I don't find much use in potions and abilities that kick in when Geralt's vitality falls below a certain point as he's already mostly dead by then. An unlucky hit can end you.You've sunk a lot of xp into Igni, which is cool, it's an uber-cool Sign and one of my favourites
You capitalise well on that particular strength at the start, let's see what we can do from there
From memory, there's a fireplace in a house upstairs, immediately before the zone point into the sewers. This is where I prepare. I'd try some proactive, offensive potions rather than defensive potions. Think of your available potions in a tiered heirarchy: long lasting, medium lasting, and short buggers. Take the longer lasting ones first, then meditate at the fireplace for an hour to reduce or zero your toxicity. Then take your medium length potions. Head into the fight, then take your short or immediate effect potions during the fight, as needed.If I'm looking for an easy fight, I stack potions like they're going out of fashion
Start with
Maribor Forest (increases maximum Endurance) and
Full Moon (increases maximum Vitality). Meditate for an hour. Take
Swallow (speeds up Vitality regeneration), then zone and head into the Zeugl fight. Quaff a
White Raffard's Decoction during the fight if necessary.As you've found, a good bout of Igni takes care of the tentacles pretty easily
As
ST_Ghost said, for the Zeugl itself, use
Strong Silver and chain your attacks (what level do you have Strong Silver at?). Also, consider a blade enhancement -
Argentia oil, diamond dust or even a grindstone. My preference is for the oil
If you're having trouble finding the Zeugl when it pops up from under the water (thereby introducing delays and allowing the Zeugl time to score a hit on you), use the Pause button when you neutralise the tentacles and rotate the camera around until you spy where it's popped up to help orient yourself.