Illaoi vs Jax Counter Pick

With 827 games logged on patch 16.13.1, this is one of the sturdier readings available for either champion, and it settles at 54.9% in Illaoi‘s favour.

• Counter Strike is a partial answer. Jax dodges basic attacks for its duration and stuns afterwards, but tentacle swings come from Illaoi’s passive rather than from her attacks, so the dodge covers less than it does against a standard duellist.
• Mixed damage cuts both ways. Grandmaster-at-Arms adds magic damage on every third strike, so her 32 magic resist matters alongside 120 armour at level 18, while Jax runs into 107.4 armour of his own.
• Base lines are close. Illaoi has 656 health and 65 attack damage, Jax 650 and 68. Both move at 350, both attack from 125, both spend mana.

Divergence appears in scaling and in what a long fight rewards. Illaoi reaches 2,611 health to his 2,401, and Relentless Assault needs consecutive attacks to build attack speed — attacks that Test of Spirit converts into self-inflicted damage while the spirit stands behind her. Difficulty sits at 5 and 4, close enough that patience outweighs mechanics. Leap Strike gives Jax the engage she cannot refuse and Empower loads the strike that follows, so the practical decision is where the fight happens: beside impassable terrain her passive has already populated, or in open ground where 68 attack damage and stacking attack speed do the arithmetic.