Passive- Battle Fury gives you fury when you Auto-attack, Crit and when you kill something, auto-attacks give you the least fury while killing stuff gives you the most, fury stacks up to 100. As fury builds up, your crit chance increases, up to 35%.
Q- Bloodlust heals for a fixed amount plus an amount scaling with your current fury, both scale with AP hence the dark seal you build in the early game. Using Q consumes your fury
W- Mocking Shout reduces the AD of nearby enemy champions and slows them if they have their backs turned.
E- Spinning Slash is a dash that deals damage, each target hit generates fury, a crit reduces Spinning Slash cooldown by 1 second.
R- Undying Rage prevents you from dying for 5 entire seconds(doesn't seem like it but its !@#$ing long) and generates fury.