So I have been playing Atomic Ivy Top... and it's soooo much fun!
Passive- If you level this first you basically cant get hurt by your oponent the sheild becoms huge really quickly and since your a tank and don't do damage, you won't see much of a decrease in damage.
Q- Just use this skill to help you farm.. Yeah thats about it... Oh it can help you farm?
W- Use as harass if you have the will. It can do some damage and the root is nice. Use it when you are getting ganked with your e to gain Movepeed and slow the enemy
E- Use this only really when you are chasing someone down to kill them or escaping a gank. The slow is very useful.
R- DO NOT USE SOLO AGAINST SOMEONE it is a waste, the passive stacks are nice and all but you waste a very strong intiate skill or escape for your teamates.