Cloud Rune + Willing Attack

[SuperHavocGuru]

So here's the situation. One of my players is a rune knight fighter and has the cloud rune.

Cloud Rune. This rune emulates the deceptive magic used by some cloud giants. While wearing or carrying an object inscribed with this rune, you have advantage on Dexterity (Sleight of Hand) checks and Charisma (Deception) checks.
In addition, when you or a creature you can see within 30 feet of you is hit by an attack roll, you can use your reaction to invoke the rune and choose a different creature within 30 feet of you, other than the attacker. The chosen creature becomes the target of the attack, using the same roll. This magic can transfer the attack's effects regardless of the attack's range. Once you invoke this rune, you can't do so again until you finish a short or long rest.

One of the things he likes to do is to stab his friend. The basic thought process is that his friend allows him to stab him in the head. Would an attack against a willing target be an auto hit? An auto crit possibly?

Also, could he land the attack and use the cloud rune to transfer the crit essentially to an enemy, giving him a free critical hit?

My gut tells me that this shouldn't work in this way, but I'm not seeing anything that says it wouldn't. He basically tries to start off every big encounter like this. I'm not worried about it being overpowered or anything, I'm just wanting other opinions on if it should work like this.

[DeTess]

You need to roll. Nowhere does it say you don't need to roll to hit against willing or defenseless targets, and the rune even specifies it uses the same roll, so no roll=no transfer. Edit: You might get advantage though.

Auto-crit on hit against defenseless targets(which is a rule) is a property of the target, not the attack, and does not transfer over.

[Unoriginal]

You need to roll. Nowhere does it say you don't need to roll to hit against willing or defenseless targets, and the rune even specifies it uses the same roll, so no roll=no transfer. Edit: You might get advantage though.

Auto-crit on hit against defenseless targets(which is a rule) is a property of the target, not the attack, and does not transfer over.

This is how I'd rule it as well.

Also, if the friend makes themselves open to the attack enough that the roll has advantage, all attacks against them have advantage until they stop doing that on their next turn.

[KorvinStarmast]

You need to roll. Nowhere does it say you don't need to roll to hit against willing or defenseless targets, and the rune even specifies it uses the same roll, so no roll=no transfer. Edit: You might get advantage though.

Auto-crit on hit against defenseless targets(which is a rule) is a property of the target, not the attack, and does not transfer over. This is the way.
That cloud giant rune can really disrupt a battle for the enemy. I've used it a lot with my rune knight fighter.

[Dr.Samurai]

You need to roll. Nowhere does it say you don't need to roll to hit against willing or defenseless targets, and the rune even specifies it uses the same roll, so no roll=no transfer. Edit: You might get advantage though.

Auto-crit on hit against defenseless targets(which is a rule) is a property of the target, not the attack, and does not transfer over.
I agree with this; the Rune specifically says to use the same roll. Generally when something is an auto-crit, it tells you "if you hit", meaning you need to roll. That roll is what carries over to the new target, not necessarily the critical hit which would be a function of the conditions on the original target.

This is how I'd rule it as well.

Also, if the friend makes themselves open to the attack enough that the roll has advantage, all attacks against them have advantage until they stop doing that on their next turn.
I agree with this as well. Remember, everything in a combat round is happening at the same time, so if your friend's ally is making himself defenseless, he's defenseless for that round.

This is the way.
That cloud giant rune can really disrupt a battle for the enemy. I've used it a lot with my rune knight fighter.
Also agreed.

Honestly, critical hits are not so powerful on their own to make this a worthwhile tactic. I think it would be better to negate an incoming enemy attack, instead of adding an extra critical hit die on your own regular attack. We are fighting against predominantly giants in our Friday game and forcing a giant's attack for 25 damage to hit another giant instead of me or an ally is a way better use of the Rune in my opinion than adding an extra die to my weapon attack.

[Psyren]

Agreed with the posters above, an I'll add - even if you rule that hitting an ally is automatic, that means there was no attack roll, and therefore the cloud rune won't trigger in the first place. There must have been an attack roll in order to trigger the reaction.

[Sigreid]

I agree with this; the Rune specifically says to use the same roll. Generally when something is an auto-crit, it tells you "if you hit", meaning you need to roll. That roll is what carries over to the new target, not necessarily the critical hit which would be a function of the conditions on the original target.

I agree with this as well. Remember, everything in a combat round is happening at the same time, so if your friend's ally is making himself defenseless, he's defenseless for that round.

Also agreed.

Honestly, critical hits are not so powerful on their own to make this a worthwhile tactic. I think it would be better to negate an incoming enemy attack, instead of adding an extra critical hit die on your own regular attack. We are fighting against predominantly giants in our Friday game and forcing a giant's attack for 25 damage to hit another giant instead of me or an ally is a way better use of the Rune in my opinion than adding an extra die to my weapon attack.
Well, an automatic critical hit on a mid to high level rogue's sneak attack can ruin someone's day on one round.

[Witty Username]

I would say the person stanging still would be using the help action, and the attacker would roll with advantage.

[Hairfish]

"Oh no! You've tried to be too clever and wind up deceiving yourself with trickster magics. Your attack hits both you and your friend for full damage and it's a crit. The rune explodes and casts Fog Cloud, centered on yourself, and you forget how to inscribe it for 2d4 days."

"The vision fades and you find yourself about to attack your friend, when you have the sudden feeling that if you try to be silly with the laws that govern the universe, the universe may be extremely silly with you. What do you do?"