I like this hex condition idea, but the condition could use some balancing on the spirit creature itself. I equate it to a rot. I believe rot has a removal cost of 3, so this should too. I'd rather it not count as direct damage as well. upkeep+1 is enough. Mages can't gain upkeep effects(balance), so they are immune to it i guess? i am not sure.
No attack has a chance to place 2 rots. most of them are only on an 8-9+. He could maybe do 1 hex on a 5+, but then his attack dice should become 3. He is for cursing more than killing isnt he?
if other sources of hexing come out, Noxious Wights may heal too well. it limits the future inclusion of hex effects. Grey spirit has no heal, so why does this spirit? I don't like the idea of heal, but if you want it maybe: "when Noxious Wight deals damage to a creature, it may take one direct damage to place 1 hex condition on that creature. When a creature is destroyed, Noxious Wight reconstructs damage equal to the number of hex conditions on it."
What I would do with your idea is this guy; more focused on hexes than damage and without healing. he is semi-restrained too:
12 mana. My Noxious Wight. Creature. Spirit.
Range 0-0. Full cast. Level 2 Arcane. Level 2 Dark.
/ Armor
13 health
Not unique or legendary. Upkeep 1. Incorporeal. Restrained.
Hexing Shriek: range 0-2, indirect, full action, 0 dice, no damage, 3+ Hex
Strike: melee. quick action, 4 dice. Ethereal. 1manatransfer.
Hexing Strike: melee. full action, 2 dice. Ethereal. 5+ Hex 1manatransfer.
As a move action, My Noxious Wight may pay 1 mana to teleport to any zone which as a hex condition in it.