The group attack is quite handy against the Beast, and other bosses where there are lots of minions around - as it seems to have more attacks the more enemies are around, with sufficient enemies, not a single attack can be landed on you because everything keeps getting hit. It's when you're down to 2 enemies that there's a problem - then a bit of aard is always handy to stun/coup-de-grace one of your assailants. Fighting humans is easier - igni them - enough will be standing around screaming in flames for you to deal with the rest fairly easily.

Oh, and always swallow a swallow. If things get really nasty, blizzard helps a lot. Of course, if you have the potions, and the preparation time, take a whole cocktail (don't forget to use albedo potions so they stack better).

Spoiler Alert, click show to read: 
Only on medium, but the final boss (Wild Hunt) I took down in seconds, having taken swallow, tawny owl, shrike (damages those that damage you - handy against hard hitting enemies), moon rise (I forget the name - the one that doubles hp), the one that increases critical hits, possibly a couple of others. And oiled up my blade. Heh, I was hitting him with strings of 400+ damage.


Generally, I don't tend to bother with the fast style - group for large masses, strong for individuals - if they're hard to hit, flame them - the resulting pain will slow them down enough to whack. Or just knock 'em down and give them a coup de grace.

Spoiler Alert, click show to read: 
Another handy spell - Quen - the shield spell. Whilst battling the striga, I found that, charged up, it can result in dealing back a lot of damage - I was almost worried I'd kill it by accident. And that was only at level 2 of the spell...