Dying Light's big expansion, The Following, is out on February 9, and at the same time the game is being released as an Enhanced Edition. But for players that don't have/want to buy the new expansion, there are still some free updates coming up. One of these updates is based around legendary skills.
Legendary skills become available as soon as the player has maxed out one of their skill trees. From that point onwards all the skill points from that skill tree are instead counted to the legendary skill tree. It's a brand new set of skills, and there are over 250 of them in total. Of course this doesn't mean that there are 250 different ones, as one skill will have many levels. Every 25 levels a player will also get new emblems, outfits and new weapons.