This is my first attempt at a guide. Any useful and helpful comments are welcomed and appreciated. I will work on updating this guide as I find better ways to play this champion.

My feelings on Yorick are that he is a beefy DPS but instead of being the carry is going to be getting more assists. Yoricks abilities are good for team fights but he can be shut down fairly easy.

The work of gravediggers is essential amongst the living, but invaluable in the Shadow Isles. There are many shades of death there, and each is embraced rather than feared or reviled. One can only ascend from one state to the next with the magical aid of a skilled professional. At the end of the first Rune War, Yorick Mori made his living as a gravedigger. His family owned and maintained the Final Rest Memorial, one of the oldest cemeteries in Valoran. The shovel he employed for his work had been passed down for generations. Each gravedigger taught his son that this shovel was imbued with the spirit of every forefather, and that those spirits would protect him during the long lonely nights amongst the tombstones. To his eternal regret, Yorick died without an heir, bringing the proud Mori line to a close. His body was interred with his shovel in the family mausoleum, and the Final Rest Memorial soon fell to ruin. Death, however, was not the end Yorick had expected.
Yorick emerged on the haunted shores of the Shadow Isles – not quite dead, definitely not alive – still clutching his beloved shovel. He soon learned that with it he could act as a ferryman for the Isles' undead denizens, helping them climb death's many-tiered ladder. This proved a curse, as a gravedigger must "bury his quota" before he too can ascend, or so the legend goes. No one knows what "his quota" is. Yorick dug tirelessly, waiting in vain for the day when he would be freed of his burden. As decades turned to centuries, the shame of his failures came to a head. He returned to Valoran to find his corpse, convinced that salvation might be buried with it. When he arrived, no trace remained of either the mausoleum or the memorial. Hope nearly lost, he discovered the League of Legends, and there saw an opportunity to immortalize the family name he allowed to be forgotten ages ago.

"Die first, then we’ll talk." -- Yorick

Pros:

Good Lane Survivability
Abilities very spam-able late game
Good support abilities (Slow and Ult)
Can Push with success
Good Damage

Cons:

Mana hungry early game
Easy to harass
Very slow

Passive - Unholy Covenant: Yorick's attacks deal 5% more damage for each summon that is active. Meanwhile, Yorick's ghouls deal 30% of Yorick’s attack damage and have 30% of his total health.

(Q) Omen of War: Yorick's next attack will deal bonus physical damage and summon a Spectral Ghoul that deals additional damage and moves faster than Yorick's other ghouls. While the Spectral Ghoul is alive, Yorick moves faster as well.

The ratio for this is 1:1 to your TOTAL AD not bonus AD.

(W) Omen of Pestilence: Yorick summons a Decaying Ghoul that arrives with a violent explosion, dealing damage and slowing nearby enemies for 1.5 second. While the Decaying Ghoul remains alive, nearby enemies continue to be slowed.

The ratio for this is 0.8:1 to your BONUS AD.

(E) Omen of Pestilence: Yorick steals life from his target and summons a Ravenous Ghoul that heals Yorick for the damage it deals.

The ratio for this is 1.2:1 to your BONUS AD.

(R) Omen of Death: Yorick conjures a revenant in the image of one of his allies. If his ally dies while its revenant is alive, the revenant sacrifices itself to reanimate them and give them time to enact vengeance.

Important note one Yorick's Ult. the revenant will only revive the hero it was cast on. So if you use it on say Ashe but Yorick dies the Ashe Revenant will not bring Yorick back.

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I start off with a Meki Pendant and 2 health potions because Yorick currently has some mana issues and is easily harassed early game. The Meki Pendant should be built into Tear of the Goddess the first time you back and you should possibly be getting Boots then too.

The reason for the Mana Manipulater is for the MP5 and eventual upgrade into Soul Shroud. IF YOU HAVE A SUPPORT who gets this dont worry about it. The Soul Shroud is good for a health, MP5, and CDR. (Some of Yoricks main problems.)

I get the Avarice Blade early for the extra gold income. It helps if you are having trouble farming. Upgraded into Ghostblade is useful for the active which will make Yorick a scary monster in team fights.

Upgrade into CDR boots. Need more CDR for more ghouls.

Manamune because it is Yoricks bread and butter right now. He spams spells and is AD based. What else do you want?

I end with Frozen Mallet. The slow, health, and damage make it a beautiful weapon.

Last whisper because more damage = more fun.

Ideally you will be in lane with a range hero because if Yorick is in a double melee lane you will be harassed into the dirt and zoned out of creep area.

DONT! Spam your abilities. Only use your E (Omen of Famine) if you are low on hp. Make sure to cast it on a minion with high hp because once the minion that it was summoned on it will run at the closest enemy hero and try to attack it and will normally die before reaching them thus you lost mana and some HP gain. I've debated over getting W (Omen of Pestilence) second because of it being another ranged ability but its cast area is small.

Everything else is basically like every other hero. Last hit minions but dont right click them back to the tower.

By the time team fights start you will hopefully have both Manamune and Soul Shroud. You should be focused on casting your Omen of Pestilence behind the enemy so they dont try to run away. Then you should be close enough to an enemy to use your Q (Omen of War) and do more damage. Then summon your Omen of Famine so you get your health back. Try to have all your ghouls up all the time during the team fight so your passive keeps your attack speed boosted.

Now as for Yoricks Ult Omen of Death this is personal preference. I personally prefer using it early casting it on our carry because then you basically have TWO carries attacking and if the real one should die they can come back for up to 10 seconds and seek revenge. Other people may prefer to wait to use it on someone who is about to die but I feel if you use it early then that death may have been able to be prevented.