Legends such as Mutiny, Insolence, etc. have a better chance of being dropped at floors 190-200 due to the deceased amount of possible legends at those floors. Eternal items and Crystal items have a 1% chance to drop, which means that every one hundred items you obtain, you will get one Eternal/Crystal legend. To increase these odds, the affixes Crystalline and Eternalized will help, however unnoticeable it is, increase these odds drastically. At rank (5), which is what wearing a Nadroji Crystal and Stone of Nadroji well bring the sets “Eternalized” and “Crystalline” to, your chance of obtaining a Crystal/Eternal legend will increase to 3.5%. While using “Nadroji” at rank (6), which is what the same item combo will bring these sets to, your odds will increase to 4.25%. These odds are also separate, so if you just use Crystalline (5), your odds for Eternal items will still be 1%. Nadroji, however, increases both of the chances. So, with Nadroji alone, your odds will increase to 1.75% with both jewelry pieces. The easiest way to obtain Eternal items is to complete the Mythic Enemy feat. To do this much more quickly, you’ll need a Hunter Ring, which you can learn about here:
Of course, when 2.1 update arrives, there’s is an ascension perk called “Hunter”, which does the same as the ring, without the ring.
There’s also another perk for Crystal and Eternal Legends.
You can read about ascension perks here: