• Gimmick Box [ID 100000212]
Gained ATK equal to monster's original ATK, but would gain ATK equal to current ATK (damage you would have take).

I'm just gonna take the wikia card text and compare it to the card's script...

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I'm just gonna take the wikia card text and compare it to the card's script...

Gimmick Box 
During damage calculation, if either player would take battle damage: Reduce that damage to 0, then Special Summon this card as a Monster Card (Machine-Type/DARK/Level 8/ATK ?/DEF 0). (This card is also still treated as a Trap Card.) This card's ATK is equal to the amount of damage reduced to 0 by this effect.

I would take 2100 damage (1900 ATK + 200 boost), but Gimmick Box gained only 1900 ATK.

I just realized, in YGoPro, there is no way to check the changed damage or the "final" damage. You can only check what would originally (battle) take and IF you have already taken it, nothing in between. Sorry.

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Huh? But what happens with cards that prevent or reduce the damage? They don't check the final damage to effect the calculation?

Reduction Barrier [511000417] also doesn't count possible bonus ATK? And Spell of Pain [511001785] and Rainbow Life [34002992]? Return Damage [511000955] is in the same Gimmick Box's boat.

Huh? But what happens with cards that prevent or reduce the damage? They don't check the final damage to effect the calculation?

Reduction Barrier [511000417] also doesn't count possible bonus ATK? And Spell of Pain [511001785] and Rainbow Life [34002992]? Return Damage [511000955] is in the same Gimmick Box's boat.

Nope, I guess not. That's why such a situation like below would happen, there's nothing we could do about it as of now.

1. Player A gains an Effect A that halves all battle damage this turn.
2. Monster A can inflict battle damage to both players.
3. Let's say Monster A can inflict 3000 damage.
4. Player A because of Effect A takes 1500 damage while Player B still takes 3000 damage.

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So please, changes the cards texts for that players know what actually occurs in the effects resolution. If you program the card in a way but it works of other, is logical that this should be reported in text so that we don't think that it is a mistake.