Passive: Relentless Assault
Basic attacks increase Jax's attack speed by 4% / 6% / 8% / 10% / 12% / 14%. Relentless Assault lasts for 2.5 seconds and stacks up to 6 times.
What makes Jax so good when fights come to standing around swinging at each other.
Q: Leap Strike
Active: Jax leaps to target unit, dealing damage if the target is an enemy.
Physical damage: 70 / 110 / 150 / 190 / 230 (+ 60% AP) (+ 100% bonus AD)
Cooldown: 10 / 9 / 8 / 7 / 6
Cost: 65 mana
Great ability all around. Offers a great way to initiate, chase, and escape all in one. Mana is low enough to usually be available, but high enough that you typically won't spam it for farming.
Active: Jax's next basic attack or Leap Strike within the next 10 seconds deals additional damage. Empower resets the autoattack timer.
Magic damage: 40 / 75 / 110 / 145 / 180 (+ 60% AP)
Cooldown: 7 / 6 / 5 / 4 / 3
Cost: 30 mana
Pretty much THE reason Jax is so powerful in dueling. Empower gives a huge nuke on a short CD, has a tiny mana cost, resets your auto-attack timer, and adds a stack of Relentless Assault to boot! What's not to love? Apply liberally in all situations.
E: Counter Strike
Active: For up to 2 seconds, Jax dodges all basic attacks and takes 25% less damage from area of effect abilities. At the end of the duration or if Counter Strike is activated again, Jax deals damage and stuns nearby enemies for 1 second. This spell deals 20% additional damage for each attack dodged to a maximum of 100% increased damage.
Physical damage: 50 / 75 / 100 / 125 / 150 (+ 50% bonus AD)
Maximum damage: 100 / 150 / 200 / 250 / 300 (+ 100% bonus AD)
Cooldown: 18 / 16 / 14 / 12 / 10
Cost: 70 / 75 / 80 / 85 / 90 mana
Well that's a block of text. Basically, press Counter Strike when you 1) are going to be fighting a champion toe-to-toe and want to make his auto-attacks worthless; and/or 2) Need to stun a target. Take note of the mana cost and the short cooldown between the first and second activation.
R: Grandmaster's Might
Passive: Jax deals additional damage on every third basic attack. The counter will reset if he does not attack for 2.5 seconds.
Magic damage: 100 / 160 / 220 (+ 70% AP)
Active: Jax gains bonus armor and magic resist for 8 seconds.
Armor bonus: 25 / 35 / 45 (+ 30% bonus AD)
Magic resist bonus: 25 / 35 / 45 (+ 20% AP)
Cost: 100 mana
Hard to read, easy to understand. Putting points in this adds a free nuke on every 3rd hit. Press R when opponents are hitting you extra armor & MR.
Note to those new to Jax:
Jax has a somewhat unique skill set where all of his abilities benefit from AD, and 3/4 of his abilities (all but counter strike) benefit from AP. Between his ult and passive, attack speed is also vastly important as you want to build up Relentless Assault stacks as quickly as possible in order to to get more Grandmaster's Might procs off as quickly as possible (Also making attack damage more important). This makes all 3 stats incredibly important to the character, so keep that in mind as you play him and experiment with items.