Fits the theme and gives Varus an interesting niche. Could be enough to take him up a notch. I don't see why not.
Also giving him a useful passive would help too. Something that restores mana would help tremendously in lane.
And even if he gets over buffed, his kit is easily balanceable and he has enough weaknesses to capitalize on. Cough no mobility cough
nah m8
no buffs to immobile champions, they don't make LC$BIGPLAY$
Although the entangle is an interesting (and thematically matching) idea, I wonder if giving and ADC a reliable blind might be too strong. Yes Quinn and Teemo have them but Quinn's is a skill shot that can be blocked by minions, and Teemo is inherently weak that he can get away with a point and click.
As for his passive, I would just swap it with blighted quiver. That becomes his passive, while his w becomes a more reliable attack speed steroid of some sort.
