Hello fellow DMs,

I’m running a one-shot adventure with players who wanted to try epic play in 5E. It will be a nice learning experience for me as well. I let them create PCs above level 20 and let them take epic boons. One player took the boon of invincibility. I will be converting Kerleth’s Tower from 3rd edition Epic Level Handbook and, in it, there is a balor with a vorpal sword.

I just want to know how you would tackle the beheading effect of the vorpal sword against the boon of invincibility. Is the beheading effect considered as a damage source and then be nullified by the boon or is the latter not applicable in this case? Or would you judge an epic character equivalent to a legendary monster and thus immune to the beheading effect?

Thanks in advance. I just want to make sure that a lucky roll on my part doesn’t instantly kill a PC if it is not warranted. 

RAW, the sword would probably cut through the boon. However, logically speaking, it probably shouldn't, since the vorpal sword is dealing damage, in the form of severing one's head from their shoulders, and the boon allows you to avoid damage.

Creatures that are immune to slashing damage are immune to the vorpal effect, and boon of invincibility is equivalent to damage immunity (though it does not use that wording), so I would rule that it can be used.

Thanks for the quick answers!

The boon is very powerful as it enables the character to negate any amount of damage from any single source, which can be a lot. It’s effect is as powerful as that of many legendary actions. Where it seems less powerful I think is that it does not become available again at the beginning of the PC’s next turn. On the other hand, it can be used while incapacitated or surprised.

The confusing wording of the boon is indeed part of the problem in adjudicating its effect.

For now, I would be inclined to make the boon work against the beheading but as this means it is spent,  it would not be available to negate the sword damage including the additional slashing damage (6d8 x2).

I would prioritize the Vorpal Sword over the Boon of Invincibility.

The Vorpal Sword effectively imposes a "beheaded" condition to a creature with a head, rather than dealing damage. Invincibility to a single instance of damage would be inadequate. Even a Hydra dies if all of its head are removed before it can regenerate. The Vorpal Sword is supposed to be the quintessential weapon, so it shouldn't be negated unless plot armor is in play.

However, if it's an issue, you could always grant them an item, or contingency effect, that reattaches their head for them. Having a weakness is a great narrative tool that even icons like Superman have. Could get awfully boring if you can't make the player quake in their boots.

Thank you for your answer.

I agree with you that it could be seen as « unfair » (for lack of a better word) to the story to nerf the vorpal sword just for the sake of avoiding an unlucky and instant PC death.

Part of my point was more that an epic PC is much like a legendary monster (epic boons vs legendary actions) and as such might be ruled as being immune to the beheading effect but still vulnerable to the additional slashing damage.

If you filter monsters by "Legendary", and sort by lowest CR, you'll find monsters as low as 3rd level with Legendary Actions.
Similarly, you can find opponents as high as CR 25 that don't have legendary actions.

"Legendary Actions" are a specific mechanic designed to balance the action economy of a standard adventuring party against a singular BBEG. The restriction on Vorpal Swords not working on such targets has to do with maintaining game integrity, and shouldn't be taken as a rule to be applied to players.

It has less to do with "fairness", and more to do with the fact that D&D is a game and not a reality simulator, so some abilities and features are never meant to be available to players, even epic ones.

All good points to take into account. Thanks!

I think the Boon was  a poor choice. It only works once per combat.