[RPG] What would the 5e phrasing be for combining multiple attacks into a single attack

attackdnd-5ehomebrewmagic-items

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+42 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?

Related question (the feature after the and): Is there a way to stun a creature without using a Spell Save DC?

Best Answer

The key phrase is "extra attack", and you need a couple other changes

It's "Extra Attack" that you're talking about:

Extra Attack

Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

The number of attacks increases to three when you reach 11th level in this class and to four when you reach 20th level in this class.

And you wouldn't "forfeit" extra attack in your Attack action. You would use an Action to activate the Heavy Blow feature of your magic item (great sword), and say something like:

Heavy Blow

You can use an action to make one melee attack which, on a hit, does damage equal to the total damage you would make if you hit with this weapon using all attacks in your Extra Attack feature (if you have that feature).

The reasons I think this follows the writing style convention better are (1) magic items in 5e commonly say that "You can use an action to..." do something whereas (2) there is not really a model that I know of in 5e for a magic item having you "forfeit" your extra attacks.

From the wording I have proposed, the following should follow deductively:

  • If you use the "-5 for a +10" feature from Great Weapon Master with Heavy Blow, and you hit, the damage is the same as if you had hit with all your extra attacks using that same GWM feature.
  • If you are a Paladin, you can add the damage of at most one Branding Smite to Heavy Blow (using up a bonus action and a spell slot to do so), because that's the most you could do using your Extra Attack feature.
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