I heard about these dragons on this site and was curious to know, when do legendary dragons appear in the world? Is there a step-by-step guide to getting them to appear?
Legendary variants of dragons were added for high-level players; they begin to appear at around level 78. Once you get that high, they can be found just like any regular dragon (although they are not guaranteed to spawn): randomly in the wilderness, at word walls, et cetera.
Note that Legendary dragons were added by the Dawnguard DLC, so you'll need that.
There is a guaranteed spawn at Arcwind Point.
A legendary dragon can also always be found at Arcwind Point perching above a sarcophagus that contains either a Draugr Deathlord or a Dragon Priest.
This spawning point still requires the The Elder Scrolls V: Dawnguard DLC and level 78+. If the player dose not meet these requirements, another type of dragon will spawn at Arcwind Point.
You generally have to be lv 78 and have dawnguard installed, but their are people who have encountered them anywhere in-between lvs 50 through 77. I've seen the videos but it is extremely rare and they can spawn anywhere they can spawn in whiterun, windhelm, winter hold, excetera.
You need dawnguard and to be lvl 78+
I read the website and it said they spawn at level 78 but they can come before that. Some people found them at level 50 and I watched videos as proof. It just gets less rare when you're around their level. Blades kinda help well. Give new locations where to find all types of dragons.
At level 66 I encountered a Legendary Dragon at Winterhold. It was the first time I'd ever encountered one (and it was badass!).
I'm not sure if it is intended or not, the only mod I've got installed which might have changed it somehow is Deadly Dragons.