Abilities

Berserker Rage : (passif): For each 1% of health missing, Olaf's attack speed is increased by 1%.

This will allow you to 1vs1 anyone and to survive most team fights, it works great with hp gear.

Undertow : Damage: 65/110/165/200/245 + 30% of Attack Damage
Slow: 24 / 28 / 32 / 36 / 40 %

It used to have a ****py slow until you put 3 rank in it but now it slows for 24% at the first level so it's worth getting it when you're lvl 2 instead of Vicious Strike

Vicious Strikes : Damage: 12/18/24/30/36 (+ 0.4/0.7/1/1.3/1.6% of Max Hp)
Lifesteal: 9/12/15/18/21% Spellvamp: 9/12/15/18/21% Last 6 seconds

What can i say, i bet any melee hero in the game would love to have that ability, use it everytime, right before using reckless swing to engage and while fighting. You will spam it with reckless as much as you can.
Armor penetration/cooldown runes, masteries, your ulti (10/20/30 armor penetration) along with hp gears in this build are meant to maximize the damage and therefore the lifesteal.
You will be able to get a nice hp regen from it as soon as you are lvl 8

Reckless Swing : Damage dealt: 100/160/220/280/340
Damage taken: 40/64/88/112/136

This is the ability we will max as fast as we can (3sec cooldown only when its maxed! 2,25 with items and runes) and i guarantee you it'll be deadly effective. It has a very short cooldown we will shorten even more.
Use it to engage, use it to dps like crazy, use it to get every kills, use it.
And don't underestimate the "true damage" effect, it boost dmg like crazy.

Ragnarok(Ulti) : Immune to disables, Flat damage absorption:25/45/65
Passif : armor penetration 10/20/30

"Shaco what are you trying to do ? Stop tickling me dude"

It lasts forever, it has a fast cooldown and it has a passif armor penetration.
When you'll be lvl 6 you should win every 2vs2 in your lane, you'll be immune to disables, tank like a mad man and you will have 40(60later) armor penetration, meaning you will deal true damage with normal attacks and Vicious Strikes to most heroes, consequently maximazing the lifesteal effectivness. Everything synergize.



Summoner Spells

Ignite: You know the spell, great to finish people, great to add up dps when you're not sure you're going to win,great to disables lifestealer heroes,etc.

Ghost: I like ghost very much when i play olaf, i learned to use it both agressivily and defensivly. As olaf and especialy in this build you will have lot of HPs and your ultimate will allow you take lot of damage and will immunize you to disables so you will most likely be able to run away from anything while being low on health.

I also use it a lot to rush heroes, you deal huge amount of dmg and with your phage/frozen mallet once you rush them they won't be able to get away. you can also rush them while they're under the tower, with your ultimate you will destroy them and run away safely.

Exhaust: It can be a good alternative to ignite but honestly your phage will slow and you won't really need the blind effect since you can take heavy punishment.

Cleanse: I don't take it because of Olaf's ulti and Mercury's Treads

Lane Strategy

The delicate part are the 6 first levels. Depending on who is laning with you and who you're facing you can either get last hit on minions while using Reckless on ennemies if they come close or just back and try not to die.

Heros like ashe for exemple can be really annoying and going for her alone will just make you loose health because Olaf doesn't have any stuns or tools to engage from long distance but if your teammate harassed her you can use your ulti+ghost to run to her without being slowed by his arrows and insta kill her

Let's say most of the time you're passif until your ennemies are half hp (or more if they're squishy) than you rush them and unleashe your barbarian raw power.With phage/frozenmallet and ghost the kill will be yours.Use your ult if they don't run away and decide to engage in a 2vs2 fight (or 2vs1, you can still get a kill and run) or if you ennemy is good at dpsing (if they do run away save it for a possible tower kill (remember you can't be stun while your ulti is on))

I don't use vicious trikes to farm or heal until lvl 8 or 10 because :
1. It's not effective heal yourself until you have 3 ranks in it
2. It costs mana and there's nothing more raging than not being able to finish someone because you're Out Of Mana.

The important part is trying to stay alive until you have your ultimate

When your lane is empty/when the teamfights begin:

With your ult and phage/frozen mallet you should be able to handle anyone but always go for the squishy non-dpsmages heroes first because your ult reduce incoming damage on every hits so it'll be more effective on a physical dmg hero who will deal 500dmg with 6 hits than a mage who will deal 500dmg with 2 spells

So what does it mean ? It means you can play it shaco style and pick isolated targets or gank other lanes. I'd recommend doing this lvl 10+ , having frozen mallet is essential.

Don't hesitate to engage in a 2vs2 or a 3vs3, if the teamfight is bigger you can still engage if no one in your team does but remember to use your ulti before engaging so you can laugh at your ennemies unleashing waves of stunning spells.
Don't forget to go for the squishy first and leave when you're low hp: olaf is like udyr, he can leaves fights with 5% hp and makes everyone rage.

Armor penetration works on turrets and you have lot of hp so that makes you an effective turret destroyer, don't forget to use Vicious Strikes before attacking the turret. That's how i won some Treelines 3vs3.

Items

Why buy at the begining ?

It's meant to be used with reckless swing , I tried lot of game with Undertow as the first ability and i have to say it's not really effective, it doesnt do lot of dmg and its slow is really , really bad (undertow=16% phage=30%).
Reckless swing will be more effective to get the first kill as you will be able to deal really huge dmg when you engage and use it once more since its cooldown is really fast, if your lane mate has exhaust or if you use ghost, you'll definitly get the first kill.

It will also allow you to stay in battle for a long time(you can easly get harassed with olaf) and spam reckless swing to harass them when they come too close and/or destroy them in a fight.
& are essentials.Combined with your axe these items will allow you to keep everyone permanently slowed so you can take your time to spamm reckless swing. 700 HPs will synergize well with Vicious Strike and your passif.


Now the order you will buy these next items will most likely depend on what kind of team you are facing, to be really efficient you have to adapt.

Most of the time i take first so i can get as much health as i can from it. Don't forget the regen is also nice. Used with your 20% lifesteal from your ability it will allow you to stay alive longer making you hack'n'slash people super fast thank to your passif.