hawkeyefan
Legend
The DM can use it in the resolution system. It's baked into the ability check system very clearly. You only roll if the outcome is in doubt. The DM decides if the outcome is in doubt, or if it automatically succeeds or automatically fails. The latter two options are DM fiat. The DM decides.
It can be used in other places as well. Once the players dropped a large avalanche of boulders onto a giant in a ravine. I could have asked for damage, but I decided that the giant couldn't survive it and just declared it dead.
I should have been more specific, I meant using it in resolution of the uncertain. When things are certain one way or the other, I think it’s usually obvious… so I don’t tend to think of this use of GM Fiat as all that powerful.
Your example with the giant is a better example of the kind of thing I was imagining. An argument could be made that the giant would survive, or that it could perish… so you bypassed the typical mechanics and declared it dead.
A perfectly valid use of GM Fiat, and nothing wrong with it at all. Also, nothing that couldn’t be resolved with a die roll.
DM fiat allows the DM to step beyond the game when the limitations are inappropriate or in the way of something much better that makes as much sense or more to happen. And it's required when the game is vague or doesn't address something, which 5e does three times a day and every other Tuesday.
My question is what do you mean by “much better”?
There is no single tool that is better for resolving things. There will often be a better tool for X or Y particular instances, but those tools are highly limited to whatever specific thing they address, so are not as good overall as DM fiat.
I’m not really convinced. There’s no reason you can’t use another method in those moments, nor do I see anything intrinsic about GM Fiat that makes it superior.