Nightmare - It is kinda original, but I don't really like it that much TBH, because it does nothing when enemy is not asleep. One question though: What if the enemy is targeted by other sleeps(i.e Bane's Nightmare, Naga's Song, etc.), would this skill affect the sleeping unit(s)?
Dark Void - Kinda cool and original, though I don't quite get how the aoe sleep works. I also see forced synergy.
Shadow Walk - Best of all 4 of your skills. Balanced, original and unique, though I highly recommend to put another sub-skill that instantly end the ability.
Dream Bond - The second skill I liked, though you really need more mana cost to make it balanced.
Overall - The hero is kinda cool and awesome TBH. I liked 50% of the skill although he just needs some nerfing and buffing. If you like, can you reply to Slade