Unless they have a way to draw, they wasted that mana, revealed that card, and can't play it this turn
equip If you have an Equipment card on the battlefield, you can pay its equip cost to attach it to one of your creatures on the battlefield
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Crew 1 The Masamune Rarity: Rare TYPE: Legendary Artifact SUBTYPE: Equipment CMC: 3 Mana cost: USD: $5.85 EUR: 4.19 TIX: 0.02 EDHREC RANK: 3946 As long as equipped creature is attacking, it has first strike and must be blocked if able
This means that it continues to be attacked and can be dealt combat damage as normal
So you could Dack's Duplicate your own Mulldrifter, draw two cards, swing for three damage over defenses, and now have a 3/3 flyer out that can get bigger and bigger over time