After the buff Yorick now have more mana so he can heal a lot at the beginning so he very strong in Early game

Iin late game "Q" deal a ton of dmg so if you have armor pen than you will totally own squishies champs. He also need mana in early to use "E" to harass and heal

21/0/9 will maximize your late game dmg

Yorick need a lot of damage and mana so buy manamune so you always have enough mana to heal yourself. In late game if you are either too squishy or your opponents can run fast than get ghostblade to increase your chance to survive and kill

You are a dps but your hp is pretty lame in early game so you need "E" first

Teleport: Very good for farming and also help out your teammates with your slow
Ghost: You need to hit with "Q" in order to get speed boost so having ghost can help you run to your opponent and hit him with "Q"

Pro
Harass and heal easily
Have all it need to be a ganker : Slow and haste
Deal nice dmg with "Q"
Ulti will help you deal tons of dmg after you died
Cons
Need mana
If you don't build him tank then his hp will be pretty low
"Q" need to be hit in order to get haste and chase
Ghouls deal lame damage

Let the initiator(s) go first and then you slow your opponents. Than if you have the highest damage in your team use ulti on yourself or else use it on the highest damage champion in your team.