How to obtain
Thundercleaver can currently be obtained only through chests.
Thundercleaver's ability is Improved Cleave which increases your Cleave Damage by 50%.
The damage bonus stacks with your current Cleave Damage.
Also works on heroes with splash damage, such as Howitzer.
Thundercleaver also has a secondary ability, Whirlwind which deals 100% basic attack damage to nearby enemy units.
Effects that apply on basic attacks/damage don't apply to Whirlwind.