Can the DM change his/her mind after a player has rolled?

Question

I'm new to D&D, and have been participating in adventures that are meant to be completed within a single night.

Last weekend, the DM requested that I make a Sleight of Hand check for an action that I wanted to perform. I rolled a 19, and the DM became visibly annoyed. After a pause, the DM said, "Actually, roll at a disadvantage, because [x] is currently happening."

I immediately thought it was unfair, but I didn't want to object, because I've only showed up to a couple of these weekend sessions. So I rolled again and had a critical miss, which pleased my DM and (obviously) annoyed me.

Question: Can a DM change their mind on the requirements for a roll after the roll has already been made?

Answer 1

Can a DM change their mind on the requirements for a roll after the roll has already been made?

Yes; they're the DM, there really isn't anything you can do to force the DM to accept the original roll.

Should a DM change their mind on the requirements for a roll after the roll has already been made?

No; especially not when it was a good roll - that's just dirty pool. If the DM forgets something as simple as advantage/disadvantage or an ad hoc modifier, they should gracefully accept the "DM error in player's favor" and keep going.

In ages past, the player-DM relationship was often adversarial; this is no longer the general case in modern gaming. The only person the DM should have an emotional response towards is themselves. They should not play favorites, either between the players or between the players and NPCs.

Answer 2

This is a bit of a grey area. As far as I'm aware, the rules don't state it precisely. From the reading that the order for an ability/skill check is:

1. The Game Master calls for an Ability/Skill check (of which she decides the DC)
2. The Player rolls

It would seem things such as advantage and disadvantage are decided in step one, before the player rolls. Obviously, your question is what happens if the GM realises or decides that advantage or disadvantage should be applied, which is not really addressed. This is something that each group needs to decide beforehand then.

However, I would suggest that your problem is not about the rules. According to what you say, you seem to think that the GM asked you to reroll at disadvantage because they didn't want you to succeed. The problem here is that the GM is calling for rolls that the players should fail. In my opinion, you should talk to your GM about this, ask them why they seemed happier about your failure than your success, and try to find a ruling on the matter for your table to apply in the future.

Answer 3

This kind of railroading is unfair, but technically allowed.

The rules on advantage/disadvantage suggest that advantage/disadvantage is applied when the roll is made, not afterward (PHB p.173, highlighting mine):

Sometimes a special ability or spell tells you that you have advantage or disadvantage on an ability check, a saving throw, or an attack roll. When that happens, you roll a second d20 when you make the roll.

The advantage/disadvantage rules in the Dungeon Master's Guide (p.239) say that the DM can impose disadvantage when something makes success less likely, but doesn't say that the DM can use it after the roll has already been made.

The situation as you describe it sounds like railroading, where the DM has an outcome in mind and intentionally prevents the players from changing the outcome to avoid ruining his carefully planned campaign. The Dungeon Master's Guide (p. 71) discourages this:

An adventure should allow the adventurers' actions and decisions to matter. Though it might resemble a novel or TV episode, an adventure needs to allow for more than one outcome. Otherwise, players can feel as if they've been railroaded—set onto a course that has only one destination, now matter how hard they try to change it.

However, the DM can, technically, ignore or change rules, make ad-hoc adjustments to the rules, and make ad-hoc rulings if they wish. The DM has the authority to do so, although with the responsibility to do so in a way that makes the game more fun for the players. As per DMG p.4:

The D&D rules help you and the other players have a good time, but the rules aren't in charge. You're the DM, and you are in charge of the game. That said, your goal isn't to slaughter the adventurers but to create a campaign world that revolves around their actions and decisions, and to keep your players coming back for more!

It may be in this case that the DM has pre-planned a plot, and your skill check, if successful, would break his plot. Many DMs are not confident in their ability to react to such plot twists on the fly, and will sometimes fail to adapt in order to keep the story going. This is technically allowed, but such a DM would benefit from learning to tell a story more flexibly.

Answer 4

There's two answers, depending on what was going on.

Option A: The circumstances genuinely warranted disadvantage.

The DM made a mistake in not applying disadvantage initially. DMs have a lot on their mind, trying to plan NPC moves, determine results of players' moves, and focus on big picture plot stuff. DMs are only human, and can make mistakes. When they do, the DM could have let you 'get away with it', or they could correct their mistake. Either approach is fine in my books - my rule of thumb for games is that if someone makes a mistake, or forgets a rule, they can undo it as long as no-one has made a decision, received information or rolled a die since the mistake occurred.

Option B: The circumstance did not genuinely warrant disadvantage

The DM's mistake is somewhat more fundamental, and they should not have tried to fix it by adding disadvantage. The DM's problem could be any of:

• They allowed a skill roll where success should have been impossible. Hopefully the DM will have learnt from this and will flat out refuse a skill check next time, or simply say that you fail even if you roll a 20.
• They prepared a significant challenge for the players, not realising it could be easily overcome with a sleight of hand roll, and the DM wasn't prepared or flexible enough to keep the adventure going for the rest of the session with that challenge bypassed. This one is hard to fix. If the DM isn't great at ad libbing and doesn't have time to prepare contingency adventures, then maybe find a DM with more free time.
• The DM considers DnD to be a competitive thing between DM and players where you consider the DM to be a neutral storyteller. If this is the case, have the group talk through their expectations, agree on common way forward to meet everyone's expectations as much as possible. Maybe try a new DM.

Answer 5

Can your DM reverse a decision? Yes. Should your DM reverse a decision? Generally speaking, no. It's unprofessional.

As a DM I try not to change my mind on anything unless it is in the players favor. Usually this occurs when a player brings up a valid rules question and the manual confirms their question. When it comes to rolls though I live with the results. It's up to me to manage the story to try to make the play session enjoyable regardless of which way the dice fall.

That said, if it was highly important to the story for you to not make the roll (i.e. the result would irreparably break the narrative) then the DM could have set the level of difficulty so high that you would not be able to make the roll, and also had you roll at disadvantage because the likelihood of you getting two natural 20s would be extremely low, or he/she should have flat out told you the feat was impossible.

A flexible, competent DM however will just close the module in a very obvious way so that the players know they've gone completely off the map, and then make it up as they go along if the players insist on abandoning the story.