Be aware that the champion threat level is based on my experience, and in game you cant Count 100% on what i have written. Becouse the threat level is ofcouse based on the opponents skills, and your skills.

When you ingage use this mechanic:

Q,E,W,R and swarm around the target with your ult on.(remember to basic attack) And if you have ignite, use that too. it will make some wild DOS.(DOS= Damege Over Secund)
Swain is a DOS champ, so as often as you can, poke your enemy with e. If you have blue, make a poke combo with e and q.
When you have Will Of The Ancients you can easy do a 2v1, just kite around and have your ult on.

This is my first guide so be nice.
I will be making lots more, so hang on :)