if my opp starts a showdown with 2 units, 4 might total, then in the action phase of the showdown, cast a Ride the wind making Kha'zix a 3rd attacker, if I win the showdown and succed as a defender in the Bf those the k6 still ready or is exhausted for the recall?

To answer your question: Kha'Zix, Mutating Horror stays in the same state he was in before being recalled.

Regarding Exhaustion Upon Recall

According to Rule 453.1 and confirmed by RiftJudge FAQs #5810, #6702, and #7084:

• A "Recall" is a specific game action where a permanent is relocated to its base (Rule 450).
• Recalls do not change the state of the permanent being recalled. Unless a card effect specifically states that a unit becomes exhausted, it retains its current ready or exhausted status.
• Because the Combat Cleanup process (Step 3: Resolution Step, Rule 461) dictates that attacking units are recalled to their base if defenders remain, Kha'Zix will be moved back to your base without his ready/exhausted status being modified by the recall itself.

Sequence of Events

1. Showdown Initiation: Your opponent initiates the showdown with 2 units (4 Might total).
2. Action Phase (Ride the Wind): Your opponent casts Ride the Wind to move Kha'Zix, Mutating Horror to the battlefield as a 3rd attacker.
3. Combat Damage Step: Combat damage is dealt. Based on your scenario, you win the showdown and succeed as a defender (meaning you have units remaining while your opponent's units are defeated/recalled).
4. Combat Cleanup (Step 3, Rule 461.1.a.2): Because you are the defender and still have units present at the battlefield, any remaining attacking units (including Kha'Zix) are Recalled to their controller's base.
5. State Retention: Upon arrival at the base, Kha'Zix remains in the exact same state (ready or exhausted) he held immediately prior to the recall.

This is my interpretation based on the mechanics of "Recall" defined in Rule 453.1 and the clarification provided in related RiftJudge FAQs (e.g., #6702). No official FAQ specifically citing "Kha'Zix exhaustion during recall" exists, but the game-wide rule for Recalls is consistent across all unit types.