I've been playing a Mage build on Dark Mode and was really enjoying it . . . until I hit Endless Battle. I'm not certain that I've encountered anything more frustrating in the twenty years or so that I've been playing video games.
Specifically, the two sections where you have to fight without any of your Witcher abilities (the first one with the 3 knights and the draugir, and the Seltkirk section) are screamingly, hair pullingly difficult. You die in 3 or 4 hits, maximum, you have zero mobility, and parry is worthless because you lose health even when you parry. In the Seltkirk section you have to kill two sets of 3 and then 4 enemies --- without the ability to save in between!!! I suppose it's possible that having the ability to counterattack off the block would make this easier, but two out of three possible builds don't have that ability.
Completely ruined this playthrough for me so far. There's difficult and then there's stupid, and this is stupid. Strongly considering just quitting rather than banging my head against this wall any longer (been on this section at least an hour).
The Endless Battle should be done after all the other quests have been done because any unfinished quests will be marked as Failed afterwards, and also because you may not have leveled up as much as might be useful.
Because you cannot dodge or cast signs, sword fight mechanics are important to understand and utilize. The basic sword fight skills are block and counter-attack. When you're blocking, ie your sword is raised in front of you, you should be able to block attacks from all sides, however be aware of all the enemies on the field and make sure they don't get behind you and get any backstabbing ideas. If you cannot block from all sides, unlock the skill from the Witcher Training path.
Banner Fight: you need to sword fight with patience- don't try to hack and slash. Hit enemy, block, counterattack, try to get them from the back. The important part is to counterattack at the right moment so you can get 3-4 hits in while they're stumbling. I focused on the draugir and ended the fight quickly, but it is also possible to kill all the wraiths and then deal with the draugir at the end.
Flaming Arrow sequence: if you listen, then you'll notice that there is a blow from a horn which indicates the release of the flaming arrows. This sequence is all about timing: run towards the protective wooden shields right after the flaming arrows stop, don't wait for the horn to blow. If you wait for the horn to blow, it's too late. If it's too late, your shield burns and you might as well start over. Just run to get under the next shield as soon as the arrows stop coming down.
Selkirk: Here is another part where the sword fight mechanics are utilized. You'll start by fighting three wraiths- don't rush ahead till you finish them or else you'll be fighting seven at once. Follow through with good sword fight mechanics: block and counter-attack. Try to attack them from the back. Try not to stand too close to the wooden barrier as it will be smashed by meteorites.
Draug Fight: best and most fun boss in the game. It can be really intimidating and has so many attacks. I am not sure what the Draug will do right off the bat, but here are some pointers for whatever it does.
Calls for Archers: flaming arrows will rain down on you and they will take a chunk of your HP- roll near the back of the burned house and wait for the arrows to stop.
Calls for Trebuchets: great balls of fire will fall down on you, and there's no way to predict where they might land. I think they can hit the same place twice or at least close enough for you to get hurt, so roll around, don't stay in one place.
Supernova move: Yikes. If it starts off with this, then you just got unlucky. All you can do is wait for it to stop, roll around, don't get hit by debris- it will knock you off your feet and you'll waste time getting back up while it gets closer to you. The Draug has the tendency to do the supernova move more than once in succession, so don't rush in to attack right after it ends.
Rushes in to attack you like a Golem: the most favorable move for you. The best tactic is to cast Yrden and trap him and hit him with 2-3 HEAVY attacks. Alternatively, you can dodge and do 1-2 heavy attacks on its back. You can easily finish off the Draug with three reps of the Yrden trap/heavy attack moves.
Priest: very easy- just run towards the goal and don't get hit.
Endless battle over, time for more awesome fights!
All in all, the EB is not a tough stage if you utilize the sword fight mechanics to their fullest extent. I had the Oathbreaker outfit, and had invested in footwork, riposte, and parry skills.