'Crowbar' card

A monster equipped with this card increases its ATK by 200 x the number of times it has declared an attack on a face down monster.

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#2 in the Half Life series is Gordan Freeman's trusty crowbar. While it offers no immediate boost to ATK (or anything else for that matter), its bonus grows over time. This thing is especially brutal because the Half Life set is going to be brimming with flip effect monsters and monsters with high DEF. As to the later, Gordan will simply be able to pound away at any defense position monster until his ATK rises so ridiculously high that he can destroy it. It's a long term weapon, but not one that should be ignored!