There's no exit portal and they can come from anywhere at all, with no tell. They distort space-time enough that they strike before the tail makes it through the portal.
There’s a little glowing ball thing that appears where the tail is going to strike actually. I never noticed until literally just not, after watching it in a video.
It’s hard to notice in the middle of the action but it’s there. Plus, thor can still just try to dodge it anyways if that’s not a good enough tell, because at least he can assume that when it does the tail thing, it’s going to come at him from some direction at his location, so all he needs to do is move away from where he currently is in. And if that doesn’t work, I don’t think it’ll just run him through because the space-time manip only applies mainly to it’s claws and teeth(?), no? Please correct me if I’m wrong. Though anyways, thor could then predict and learn how to dodge the attack again from the first time after it uses it on him, since it doesn’t majorly change up how it does the attack.
For getting hit by claws and bifrost? Well, of course he’s not going to be completely able to dodge EVERYTHING nidhogg throws at him. And Yknow what, I apologize if I made it seem like that’s what I was saying, but I think thor will be alright. The claws will go through him because thor has resistance to jack shit but, it’s technically not an instant kill depending on how it hits him, and he has pretty good endurance to being hit by normally lethally damage. For the bifrost, it’s not really an instant kill either. It’ll hurt him if the explosion is triggered, but he probably won’t be down for the count from getting hit by a couple of them. If anything, thor has a more reliable elemental attack that he could use to end the fight quickly if he needs to IMO; his lightning and electricity. Nidhogg does not have a resistance to that. Could possibly electrocute her to death pretty quickly.
The moves are telegraphed because you, the player, have to react to them.
Saying that it's dodgeable in gameplay where of course it has to be avoidable with your limited movement speed and maneuvers isn't that great of a support.
This is true, but gameplay is 90% of what we get from nidhogg as reference for how it fights, and for a good portion of her attacks, they’re telegraphed. Not even crazy telegraphed either like a Nintendo boss or something. Just telegraphed enough that thor should able to see a good amount of those attacks coming.