This skill has been ported very incorrectly, with:
Incorrect movespeed when movement speed increasing items are equipped
Incorrect interaction against stuns
I am not going to bother with the repro and just show it in a couple of videos.
As you can see the haunt illusion has movespeed increased with items (400 base + 100 BoT's + 10% yasha --> 550, capped at 522)
The illusion is NOT stunned when slardar uses his slithereen crush on it.
The illusion is NOT hindered by terrain or trees, and should walk through furion's sprout too (which I failed to add to the videos)
EDIT: Illusions (Haunt OR Manta etc.) (NOT summons) should also get bonus MS while moving along the dagger's path. (Tested by Appelsin) Non-haunt images will NOT lose their collision from the dagger buff. (i.e. no cliffwalking manta images )
The haunt illusion's movespeed is 400, regardless of the items it has equipped.
The illusion IS stunned when slardar uses his slithereen crush on it.
The illusion IS hindered by terrain and trees, and fails to walk through things such as sprout by furion
EDIT: Illusions (Haunt OR Manta etc.) do NOT get bonus MS when moving along the dagger's path (Tested by Appelsin)
So basically spec's haunt is broken at the moment, compared to how it used to be for combat purposes, as it's images doesn't move as fast, get hindered by terrain and can be stunned.
EDIT: Thanks to Appelsin for further testing - ALL disables should be ignored, with the EXCEPTION of:
NORMAL WORKING (Same as on heroes):
Ensnare-style skills (ensnare, spirit bear entangle)
Heaven's Halberd (and therefore assume all disarming effects)
Impales (Earth spike - Lion, Ravage on Tidehunter etc.)
All slows work the same.
DIFFERENT TO HERO INTERACTION:
Song of the siren & Nightmare which causes them to get immobilised, but still attack as normal
Hex which acts exactly as you'd expect it to act on an illusion (instant kills it, nothing new here)
Mana drain - instant death to illusions (as always)