Can Kha'Zix mutating horror trigger multiple times a turn?

Yes, Kha'Zix, Mutating Horror can trigger multiple times in a single turn.

According to his card text, the ability is a triggered ability:

"When I attack or defend, if an enemy unit is alone here, give me +2 [S] this turn and gain 2 XP."

Why it can trigger multiple times:

1. Trigger Condition: The ability triggers "When I attack or defend." Each time Kha'Zix gains the "Attacker" or "Defender" designation—such as by moving into combat or participating in different combat showdowns throughout a turn—the condition is met.
2. No "Once Per Turn" Restriction: Unlike some cards, Kha'Zix’s ability does not contain the phrase "once each turn" or any other language limiting the number of times it can trigger.
3. Independence: Each time the trigger condition is met (Kha'Zix gains the Attacker or Defender designation), the ability triggers independently. Provided the "if an enemy unit is alone here" condition is met at that time, the effect will resolve.

Important Considerations:

• Trigger Timing: As noted in the rules, combat triggers (Attack/Defend) happen the first time a unit gains the attacker or defender designation in a specific combat. If Kha'Zix were to somehow gain those designations again within the same combat, he would not trigger again. However, if he participates in a different combat later in the turn, those designations will be assigned again, allowing the ability to trigger anew.
• Condition Check: The ability is a conditional triggered ability. When the ability triggers and is placed on the chain, the game checks the "if an enemy unit is alone here" condition on execution (see Rule 359.3.f.4). If there is an enemy unit alone at the battlefield at that time, he gets the bonus and XP. If the condition is not met (e.g., your opponent has moved another unit there), the ability will still resolve, but it will have no effect.