Personally, I love the idea of an ethereal champion who can phase in and out of existance, and have tried to make something similar to this myself, with an enchanter linking allies together and sharing damage/buffs. However, as I found out, there is a few issues that both our kits produce.
Passive:
This is poses many issues with some interractions, as well as a core mechanical flaw.
What happens if the ally (assuming thats what you meant) goes afk? are you stuck in fountain for 5 minutes?
And how about if they teleport or something like that? are you just dragged along for the ride to the nearest new spot?
As for the core issue, alot of the value is in the fact this champion is invulnerable. Which caused enough issues with Yuumi, who is simply untargetable. Things like turrets and applied DoT still effected her, this champion can freely run under tower at any point of the game.
Second of all, this champion is FORCED into being a support. It is basically a more extreme version of Yuumi.
It also makes this champion completely un-interractive. It is basically a mobile buff, players will just think along the lines of "dont fight the buffed person solo" and thats the only counterplay needed.
Q:
All I can think of is boosting strategies. Especially since there is no point getting scaling, this champion simply has to get enough mana regen to be able to have this on all the time, then there is nothing else the champion really does.
Imagine a Yi, with a permanent, untargetable lulu on him.
How about a jax who gets +100 armor/Mr with his ult and then 600AD and 500AP and oneshots everyone while being unkillable.
W:
Honestly isn't too bad. But could become way too overpowering. Along with a support item, trinket, and control wards. This champion can permanantly have 9 wards up at one time. Which can make the game unplayable for enemies since their location will always be known.
E:
The biggest issue with this is that she can go anywhere with it. What if she just runs under an enemy tower and snares a recalling enemy every 5 seconds?
Or she can simply walk up to the enemy carries and snare them for no penalty. The only counterplay to this is to predict the E and flash it.
R:
Biggest
Trolling
Tool
Ever.
Overall, this champion is little more than a variable buff with annoying feautures. While I like the idea, this isnt the way to go about it.