During damage calculation, if your opponent's monster attacks (Quick Effect): You can discard this card; you take no battle damage from that battle.
Rulings
Netrep Rulings
Discarding "Kuriboh" is a cost of using "Kuriboh's" effect.
Discarding "Kuriboh" is considered playing "Kuriboh."
"Kuriboh" will reduce all overflow damage to 0, regardless of any cards played during the Damage Step.
"Kuriboh's" effect is not a targeting effect.
Netrep Q&As
Q: Can "Kuriboh" be used after "Injection Fairy Lily" uses its effect to boost the ATK? A: "Kuriboh" CAN be used to reduce the damage from "Injection Fairy Lily" to 0, even after "Injection Fairy Lily's" effect has been used in the Damage Step. Steve Okegawa, 12/07/2003
Q: Player A plays "Injection Fairy Lily" and declares the use of effect. Player B discards a "Kuriboh," flips a "Waboku," etc. Does Player A still take the 2000 points of damage for the use of effect? A: You can discard "Kuriboh" during the damage step after "Injection Fairy Lily's" effect has been activated. The player that activated "Injection Fairy Lily's" effect will still pay 2000 Life Points and increase her attack by 3000. You cannot activate "Waboku" during the Damage Step. The cost for "Injection Fairy Lily" is just that, a cost. It is not "damage". Curtis Schultz, 12/04/2003
Each time this card inflicts Battle Damage to your opponent's Life Points, you can remove from play up to 2 Monster Cards in your opponent's Graveyard. As long as this card remains face-up on the field, your opponent cannot remove from play any cards in either Graveyard.
Effects that remove cards from the Field, Hand, or Deck from play may be used if "Kycoo the Ghost Destroyer" is active on the field.
If "Kycoo the Ghost Destroyer" destroys a monster and inflicts Battle Damage, the monster destroyed is not an eligible target for "Kycoo the Ghost Destroyer's" effect.
Q: Can my opponent play cards like "Bottomless Trap Hole" or "Nobleman of Crossout" while "Kycoo the Ghost Destroyer" is face-up on my side of the field? A: Yes, "Bottomless Trap Hole" and "Nobleman of Crossout" do not remove cards from the graveyard and put them out of play. bishop, 12/27/2003
Individual Card FAQs
"Kuriboh" does not target the attacking monster.
"Kuriboh" only prevents Battle Damage to your Life Points; it will not prevent your monsters from being destroyed.
"Kuriboh" can only be activated while in your hand, its effect cannot be used while "Kuriboh" is on the field.
Using "Kuriboh" is a Multi-Trigger effect.
"Kuriboh" is activated during damage calculation. If your opponent attacks with "Injection Fairy Lily" and activates her effect, you can chain "Kuriboh" to reduce the damage to zero.
DARK|
Level 1|[ Fiend / Effect ]
ATK 300|
DEF 200