Orb Barrage is interesting, but I don't think that the sequential effects of the orbs track logically. Three orbs of differing sizes is interesting..; if you want to add some additional effect, there's got to be something that follows better here than these three difficult to follow effects. Astral Gate is an interesting summon ability, seeking to address the additional experience offered by increase wave pressure with some clause that biases your hero design. From here I'm looking to see a kit that further pushes the idea of this hero as a lane pusher. For the second two final abilities, I'd try to make these less focused on having a specific interaction with the character's astral minions. For the third ability, I think you could extend these benefits to regular minions / your allied heroes. I don't know if a disguise ability is the most effective synergy here, especially packaged with a minion steroid.
Essentially, what I'd be looking for is something more like... a global teleport. For example, I once designed a concept for Mephisto for Heroes of the Storm (who eventually became a character, anyhow) which had a global teleport that caused him to start losing health until he reactivated the ability, returning to his cast point. A delayed nuke projectile. Charged Bolts. And something like Warlock damage share--which could be useful as an ability cast on your allies, to prevent lane minions from dying instantly (more like Tauren Spiritwalker damage share), to causing enemies to take more damage by having them share a percent of each other's damage; or, a choice for a different ultimate, to convert a group of minions into allied minions.
If you're going to go with a minion summoner theme, you have to really push that design somehow and maximize the odds that you can push into the enemy base. Global mobility is probably the most important element there that I feel needs to be added. I think the projectile nukes on skill 1 & 4 are less important. Adding to that a better way to give minions a steroid would be a positive change, in my opinion. I wouldn't abandon the idea behind Astral Mist. I could see better mechanics lending credence to the theme there. If you're moving forward with modeling the character, consider marrying the visual elements with an improved design for the abilities.
