The Witcher:EE

[FactionHeir]

47 pages of discussion and solutions
http://www.thewitcher.com/forum/index.php?topic=2424.0

My personal way of doing it is wait till its about 22:00 in the cave, coat your steel blade with specter oil, drink a nigredo and a rubedo one. Best would be tawny owl and swallow, see which ingredients you can get most easily for either to make the above.

Then go out, quickly click yourself through the cutscene (as time runs in the background and thus your potions too) and start off with steel group style (be sure to change to that before you leave the cave, as changing style after drawing your weapon makes you lose time). Use it to attack the beast and once the barghests around it are mostly dead, swap to strong style and hit it. You can use an aard in between if things get messy, but shouldn't have to. Igni won't do much on the other hand.

You can of course also do it the cheesy way and touch a place of power and a circle of wind before entering the cave at about 20:00 or later and then just blast the beast with an aard (you would have to have focussed you build on it though) for a 1-hit kill.