What would the 5e phrasing be for combining multiple attacks into a single attack?
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A (homebrew) magic greatsword has this feature: Heavy Blow. When you take the Attack action on your turn, you may choose to forfeit your attacks for one very powerful attack. The powerful attack uses the lowest modifier in the attacks you forfeit. If you hit with this very powerful attack, you deal damage as if you had hit every attack you forfeit, and [...] The intended behavior is that an 11th level fighter with a +8 to hit would be able to use his action to make a single attack with a +8 to hit, dealing 6d6+12 damage on a hit (2d6*3+STR*3). If this fighter has great weapon master, then the attack would be a +3 to hit to deal 6d6+32 damage on a hit (2d6*3+STR*3+10*3). How would an effect like this be implemented to most accurately follow the design conventions of 5e?
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