Hello and welcome to my guide Maokai. Maokai is a champion like non-other in League of Legends, as he is a Mage-Tank. He also happens to be a tree. I have presented two different versions of Maokai: A more tank-focused one and a more Mage-focused one.

Tank
Lots of armour and magic resist
More health than other build
Tends to make more gold via assists
Slightly cheaper build
Stronger late game

Mage
Higher ability power/damage
Ultimate is devastating if used right
Can get more kills early/mid game
Squishier
More expensive

Maokai becomes very durable late game, and his roots and slows make him quite able to ***its your carries in getting kills, and his ult can change teamfights. This build makes Maokai a pain to kill late game, and a good filler of the "tank" role. Maokai tanks using his slow and roots to control enemies in the lane, and protecting his Teamates during large fights. Unlike many tanks, Maokai lacks a Initiating ability, and instead has a strong harasser. Honestly, I believe that Tank Maokai is stronger and better suited for team play, but I like to have options ;)

Maokai's early game bursting is quite good, and while laning he can mow down careless enemies very well. The harass, root, slow and repeat combo gets kills fairly easily, and makes Maokai an really, really annoying person to lane against (I seem to get called a F***K and a P**SY a lot with this build). While this all may seem great, by late game Maokai just cant do as much damage, and instead your more of a random tree who helps focus down fleeing enemies.

Arcane Smash Arcane Smash provides some magic damage and a slow in a short AOE in front of you. This is what you use to chase enemies, deal same damage, and slow enemies chasing you or your allies.
Twisted Advance causes you to rush forward and root the enemy while dealing some damage. The move is great for chasing a moving foe, or jumping forward to start a fight. This move can be used to initiate a team fight, but honestly I think that AD carries are better initiators.
This ability is why I love Maokai, it has so many uses. It can: last hit minions, harass from behind turrets, check bushes, it also does quite good damage when it explodes.
Maokai's ultimate is a perfect tank ult. As long as your team stays in it, they take 20% less damage on top of any armor or magic resist they may have. The important thing to remember is to hit the "R" key again to release the damage. While its damage isn't great by itself, when timed right it can hit the entire enemy team for some hefty magic damage. The trick is waiting long enough to charge it up, but releasing it once you think you've hit its maximum. This spell is guaranteed to get you a lot of assists.