@Riot, Jax is bugged with fervor of battle and doesn't stack correctly
Damaging champions with melee autoattacks grants two stacks and damaging champions with spells grants two stacks also, up to a max of 10 times.
Jax's W, Q, E, and R all count as spells, not normal AA on hits, because they all proc spellvamp. Yes, this is the case, according to Riot, the wiki, and how spellvamp works, this is an undisputable fact.
However, Using Q and W together on an enemy champion only grants two stacks (should grant 4), nvm about this one because of the 2 second cooldown thing
Hitting an enemy champion with empower grants only two stacks (should grant 4 because melee AA + spell)
Hitting an enemy champion with an ultimate proc only grants two stacks (should technically be 4 because melee AA + spell)
Needs to be fixed or change the tooltip