Each ability has too many layers baseline. Simpler is better, you can make a complex character without all of this.

Embrace your Rage being random doesn't seem like a good idea.

Cool concept and kit, however I have some criticism. - His trait seems a bit too strong. a 5 second 20% slow and attack speed slow is way too good, since it can stack up to 40%, and apply a 1.5 second root. I propose maybe reducing the slow percentage to 10%. - Q ability kind of perplexes me. Does it passively grant 50% bonus attack damage against slowed, rooted or stunned enemies? If so, state it as a passive. - W ability is cool, but I think the cooldown is a bit too low, maybe...

Sounds like a good change! Thank you for the feedback.

If I had to say, I think Millhouse would be better with a normal mount instead of a short range teleport. If he can't mount, that would make him very inferior.

It's cool, but the charging heroic is too similar to water elemental in my opinion.

I like this concept, but to further understand it, it would be nice if you added stats and basic-attack stats.

Chilling Maw does not really seem like a good heroic. It doesn't grant any power spike for Sapphiron at lvl 10. I'd suggest since the other heroic is more of a damage/trait related heroic, that you should replace Chilling Maw with some kind of CC or terrain-related heroic. The abilities should also get mana costs. Other than that, I like this concept. Also, shouldn't the mount grant 30% movement speed? Diablo's class-specific mount increases Diablo's movement speed to 130%.

I noticed you refer to armor as a %, but it's really not. I'd suggest you change all the places you refer to armor by removing the percentage (%) symbol. Otherwise I really like this concept!

I think you should look into tweaking your numbers. If Mercy's health is 1200, she's going to be the squishiest hero in the game. With less health than pilot D.VA.