Skin note: Corrupted Ysera is basically a given and would look amazing.
I'm super excited to do this concept as I've been thinking about it for a long time. I've always been a huge fan of the Dragon aspects and, as of this time, a real Dragon has not been fully realized in Heroes of the Storm. So first and foremost, my Ysera concept is in Dragon Form, all the time.
The whole concept of Ysera, is a beefy support, that heals her allies, damages her enemies with AoE, and mitigates damage through her trait and ult.
Her "mount" is something different than any movement ability currently in the game. I wanted something that would make people think strategically about their global, and provide downsides for flying across the entire map.
Ysera's healing is mainly AoE (her Breath and Renewal), but as a twist all her healing also has the potential to damage enemies. Setting your Breath up to get maximum value, finding out you need poke and taking the Precision Flame talent, or throwing your Defile on an enemy in a key location to make a large damaging pool.
Slumber is an interesting ability. It's potentially very powerful, or completely worthless. Make the range too long, and it's easily a ganking tool. Make it too short, and you're almost assured to quickly cleave it off. So somewhere in the middle range is the goal, but would require real world testing to tune properly.
Finally the ults. I wanted to get something very thematic from both ends of the spectrum. Enter the Dream encompasses the protective aspect of Ysera, mainly used to protect your team from large, predicted incoming damage, or to potentially save them in a bad situation.
Nightmare is on the other end. I wanted a very fear inspiring ult for when your team is ready to gank a player or team. Now, because this ult is team wide, the sight reduction isn't gonna be quite to the extent of Isolation, but it will be enough to be disorienting if you're not on top of things.