During the Damage Step, (ダメージステップ, Damējisuteppu) of the Battle Phase, the damage is calculated from the declared attack. If the defending monster is face-down, it is flipped face-up first during this Phase. If the defending monster has a Flip Effect, it is applied after Damage calculation, but still within the Damage Step. The Flip Effect does not affect monsters that have already been destroyed as a result of Damage Calculation. This includes the monster itself, so a flipped "Penguin Soldier" that was destroyed in battle cannot select itself as a target since it has already been destroyed. This is because, even though the monster has not left the field, it has already been decided that the "Penguin Soldier" in question will be sent to the Graveyard.
In the Damage Step, only certain cards and effects may be activated. These include:
- Counter Trap Cards can be activated in the Damage Step as they are Spell Speed 3 (regardless of whether they affect a monster's ATK/DEF or not).
- Normal Trap Cards, Continuous Trap Cards, Quick-Play Spell Cards, and Quick Effect Monster Cards that alter the ATK and/or DEF of one or more monsters on the field ("Blast with Chain", "Rush Recklessly", "Castle Walls", "Reinforcements", "Shrink", "Honest", etc). A card that alters the ATK and/or DEF can only be activated up until the start of damage calculation. Also, the card must DIRECTLY affect ATK/DEF to be valid; you cannot activate "Scapegoat" during the Damage Step even if you control "United We Stand", for example, because "Scapegoat" does not directly change the ATK/DEF of any monsters.
- Mandatory Trigger Effects ("King Tiger Wanghu").
- Flip Monster Effects (which are mandatory by nature) ("Cyber Jar").
- Quick Effect Monster Cards that negate the activation of other cards or effects ("Herald of Perfection, "Horus the Black Flame Dragon LV8").
- Any card whose text specifically says it may be activated during the Damage Step ("Nutrient Z", "Kuriboh").
- Cards that do not meet the activation criteria, but whom Konami have stated may be activated during the Damage Step ("Null and Void").
Cards that Special Summon monsters when destroyed in battle, such as "Shining Angel", "Mystic Tomato" and "Pyramid Turtle" all Special Summon monsters during the Damage Step, and as such, "Torrential Tribute" and "Bottomless Trap Hole" cannot be used against them, since these cards cannot be activated during the Damage Step. For the same reasons, "Royal Decree" cannot be activated in response to Trap Cards like "Skull Dice" during the Damage Step, since it does not alter ATK or DEF (if Royal Decree was already face-up prior to the Damage Step, though, then it will still negate cards such as "Skull Dice" during the Damage Step). The Flip Effects of Flip Effect Monsters such as "Cyber Jar" activate after Damage calculation if flipped face-up as a result of battle, but it is still within the Damage Step, so "Royal Oppression" cannot negate it. Also, certain cards prevent the activation of Spell and/or Trap Cards until the end of this step, such as the "Ancient Gear" monsters (with the exception of "Ancient Gear" and "Ancient Gear Cannon").
"Spellbinding Circle" cannot be used in the Damage Step since it does not change the ATK or DEF of its target. However, "Shadow Spell" can be used. Although "Shadow Spell" has the same attack prevention effect as "Spellbinding Circle", it lowers its target's ATK by 700.
At the end of the Damage Step, the Monster Card(s) destroyed as a result of battle are sent to the Graveyard, unless a card effect specifies that they go elsewhere, such as when "Macro Cosmos" or "Dimensional Fissure" is active.
- Breakdown of the Battle Phase (This page also includes a detailed breakdown of the Damage Step)