Who decides whether to opt out of beneficial abilities when under Suggestion?

Question

One of my PCs is under the effect of Suggestion and attacks another PC to defend the villain (the course of action). He has Great Weapon Fighting Style:

Great Weapon Fighting

When you roll a 1 or 2 on a damage die for an attack you make with a melee weapon that you are wielding with two hands, you can reroll the die and must use the new roll, even if the new roll is a 1 or a 2.

He rolled 1 on the damage die, and I told the player to reroll it as he has the Fighting Style. He refused and wanted to opt out of it, because the PC is attacking his ally.

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Who should have the say of opting out of using the ability or not when they are under suggestion? My argument is that they are conviced to defend the villain at all cost, so logically they will use abilities to help the villain too.

Note that this not only about Great Weapon Fighting, but also includes Halfling's Lucky racial ability, Lucky feat, Portent, and other abilities/spells.

Answer 1

If the Suggestion is working, and the PC under it has decided that it is a reasonable suggestion, then honest play would indicate that the character would use whatever abilities they have to carry out the suggestion. Especially with things like that GWF reroll ability that isn't even an expendable resource — he can do it whenever it is advantageous, so there's no reason he wouldn't.

As for expendable resources, that's a judgment call, depending on how the character would behave normally. Some characters are naturally very frugal with their resources, and might not use Portent or Lucky or a Superiority Die or whatever in that situation, others may normally be more cavalier about such uses. The point is, though, that the player should play it honestly, and not try to metagame the situation and claim that the character would not do something that would be effective, just because he has been turned to the other side.

In the example, with a free resource, it's very clear that the character would have no reason not to use it. With expendable resources, more ambiguity is present.

But to answer the question directly: the player should play it as honestly as he can, and if he fails to do so, the DM may have to step in and rule on it.

Answer 2

Note that the phrasing of GWF - and most features/feats of that sort - states that you "can" do it, not that you "must". Whenever a feature/feat (including Great Weapon Fighting) is worded this way, it means that the player can choose to do the specified action/behavior, but they can also choose not to do so.

Regarding the usage of Suggestion to cause a creature to attack its ally, the description of Suggestion states:

You suggest a course of activity (limited to a sentence or two) and magically influence a creature you can see within range that can hear and understand you. Creatures that can't be Charmed are immune to this effect. The suggestion must be worded in such a manner as to make the course of action sound reasonable. Asking the creature to stab itself, throw itself onto a spear, immolate itself, or do some other obviously harmful act ends the spell.

The target must make a Wisdom saving throw. On a failed save, it pursues the course of action you described to the best of its ability. The suggested course of action can continue for the entire Duration. If the suggested activity can be completed in a shorter time, the spell ends when the subject finishes what it was asked to do.

You can also specify Conditions that will trigger a Special activity during the Duration. For example, you might suggest that a Knight give her Warhorse to the first beggar she meets. If the condition isn't met before the spell expires, the activity isn't performed.

If you or any of your companions damage the target, the spell ends.

Sage Advice does address this kind of usage of Suggestion here. In response to a question asking whether Suggestion can cause a target to attack another creature, Mike Mearls suggests:

Only in specific situations - would have to play upon existing rivalry or anger. Ex - Guy you suspect is a traitor really is.

Chris Perkins says:

It can, but if the spell's target thinks the suggested action is likely to cause it harm, the spell could fail.

One could certainly argue that you attacking an ally is likely to result in you being harmed. The caster would need to word the Suggestion carefully if they actually want it to sound reasonable.

If the caster does manage to word the Suggestion convincingly enough in just the sentence or two specified, and the target fails its Wisdom save, then it does indeed pursue the course of action to the best of its ability - which would presumably mean it would not hold back when making such an attack.

Answer 3

I mostly agree with phill's answer, but I would suggest one alternative option. If the player only barely failed his saving throw I may consider giving him a compromise by allowing him to roleplay that he is still conflicted or undecided even under the suggestion, as his natural instincts resist the the magic.

IF the character convincingly roleplayed this I may allow them to choose to be more frugal with their resources, including not doing a re-roll in this case, to represent that part of him is still resisting the suggestion and holding back.

However, I would only offer this option for certain groups, the sort that focus more on roleplaying and don't try to meta-game too much, or in general wouldn't abuse my generosity here by using it as an excuse to try to push me for even more ridiculous compromises later. I'd also only allow it in a case where they barely lost their saving throw, if they wizard casting suggestion rolled a natural 20, for example, I'd say the player was completely under their control and had to do the re-roll and otherwise play 'honestly' by using resources as they would if they were fighting enemy NPCs instead of their allies.

Ultimately though this is purely a house rule. My main reason for offering it, besides my general like the idea of rewarding roleplaying with logical mechanical advantages, is because I have a particular dislike for the save or suck/die style spells in D&D as I feel it's dissatisfying to players to have a mighty character thwarted by a single badly timed natural 1 when there was nothing they as players could have done to avoid it. I feel suggestion is particularly bad at this since I would hate to find myself having to roleplay the guy who killed his best friend because he rolled a nat 1, and so I don't mind offering some logical limitations to such spells. Of course if I allowed this for the player I would make it part of the rules for everyone, including enemy NPCs the player's may later try casting a suggestion on.