I'm back to support my statement
Night furies were feared for the fact they blended in with the night sky, they were feared for their incredible stealth and speed. ( Also people leave out the fact that there were many dragons that the vikings feared.) Unlike what people think, nowhere in the description of a night fury indicated they were feared for power or strength. People focus on night furies way more than any other dragons, the IQ for skrill and night fury is the same. There are many other smart dragons as well who have the same or more IQ than a night fury, for example the sentinel. Night furies made humans fear them but people fail to see how many dragons do NOT fear toothless. Yes he took dominance over them but they did not fear him. Personally I don't see night furies as a strong or powerful breed, I think skrill wins this.
When toothless fought the bewilder beast, it simply didn't fight back. He needed a whole army to help him fight the bewilder beast. Plus a few things I'd like to point out is the only reason he wasn't re-controlled by the bewilder beast was solely because of hiccup. Him breaking out of the ice was solely plot armor as well, he was curled up with his mouth shut and the ice suddenly broke open. Toothless gets a lot of buffs that are solely because he is main character, so there are probably a few things that regular wild night furies wouldn't have.
(Ima use words from a friend of mine on Yt)
In the first movie, for some reason (also known as plot armor) Hookfang decided to not use his fire or strength against Toothless like he did with Hiccup, aparently Hookfang's gigantic neck couldn't reach Toothless on his back, and when Toothless pushed him back, he just stood there trying to get to Hiccup instead of just yeeting Toothless into oblivion. And the Triple Stryke, AGAIN, for some reason (plot armor) didn't kill Toothless when he clearly could, the Triple Stryke grasped Toothless with one of its tails, pointed the other two tails into his face, and just stood there, giving Toothless time to shoot him. Then suddenly Toothless went bErSeRk (basically alpha mode, but before the httyd 2 story) and suddenly got really strong and fast and ""defeated"" the Triple Stryke.
He never defeated the Skrill, in fact, all of the times that the Skrill showed up, Hiccup and Toothless usually just ran away. And when Toothless actually went to fight him directly both of their shots collided and made a big explosion, and while Toothless was blown all the way to Berk, the Skrill was barely affected by the explosion.
Skrills have great vision and are known for being able to see through dark clouds even at night, and also are pretty good at tracking. Toothless takes 5-10 seconds to attract/absorb lightning and fully cloak, the Skrill could easily just absorb the lightning Toothless needs to heat up or just shoot him since Toothless needs to concentrate to absorb lightning, so he probably wouldn't pay attention.
The Skrill not only rivals the Night Fury's speed normally, he also can ride lightning bolts with seemingly no limit or difficulty (basically he uses the lightning energy to fly at hypersonic speeds) so he's at least several times faster than the speed of sound.
Toothless isn't immune to lightning, he even got exhausted after using his cloaking ability once, he only absorbed a bit of the electric energy to heat up his scales so he could be transparent for less than 10 seconds. In the Book of Dragons short, it is mentioned that the Skrill can shoot bursts of white fire, so that means the Skrill's firepower is more than just lightning. And even if it he doesn't have it or use it, it's still really high concentrations of lightning from active storms into one single shot.
(Back to my words)
The skrill also does a lot with it's lightning, it doesn't even have to shoot lightning if they are fighting near storm clouds because it can simply redirect lightning and take out multiple opponents. Night-furies are shown that they can only attract lightning from storm clouds, while a skrill stores it in their body or uses a regular cloud to ride lightning. The skrill was shown in an rtte episode that it can re-absorb it's own lightning, so IF a night fury could shoot lightning then there is a high chance that the skrill could absorb the lightning. We also see in httyd 3 when he tries to get the death grippers off, the lightning circling him doesn't affect the death grippers UNTIL a lightning bolt strikes them therefore using lightning in an offensive way is sorta useless for night-furies. While a night fury may disappear for a few seconds but it is shown they simply run away or use it to move around their enemy not fight while being invisible.
I think I covered everything but overall the skrill wins in my opinion.
