These TCG rulings were issued by Upper Deck Entertainment and have since been deemed unofficial by Konami. They were previously considered official and can still be correct, as long as they follow the official gameplay rules, or unless Konami has issued a ruling that says otherwise. References: 
This card can only be activated during your opponent's Damage Step during the "Calculate and Apply Damage" portion or at any point in the Damage Step prior to that.
You must take the 2000 points or more of Battle Damage from a single attack. If you take 1000 points of damage from one attack, and then 1200 points of damage from a second attack, the effect of this card will not activate.
If "Hayabusa Knight" attacks you directly twice, the effect of this card will not activate. The Battle Damage must come from a single attack, not a single monster attacking twice.
You can activate 2 copies of "Nutrient Z" and you will gain 8000 Life Points if you would take 2000 points or more of Battle Damage.
You cannot activate "Kuriboh" in a chain to "Nutrient Z"'s effect. The effect of "Kuriboh" would reduce the Battle Damage to 0, and then the effect of "Nutrient Z" will no longer increase you Life Points. You must actually take the damage to gain the benefit of "Nutrient Z"'s effect.