The perform skill is used to perform. Acrobatic Performer allows you to use Acrobatics instead of your perform skill, except
You can use it for the Perform action.
The scope of the Performance skill is:
You are skilled at a form of performance, using your talents to impress a crowd or make a living.
The Core Rules explicitly identify two actions within this general domain: the Perform action and the Earn Income trained action.
Acrobatic Performer allows you to use Acrobatics instead of the Perform action. The Perform action has a fully described resolution path. On a success or critical success, the observers are pleased with your performance.
Performance skill feats
One Performance skill feat explicitly uses the Perform action. Fascinating Performance allows you to fascinate 1 observer.
Two others (Distracting Performance and Impressive Performance) reference the Performance skill, but do not refer to any specific action. Consult your GM to decide whether you can apply Acrobatic Performer or not.
Lowering Diplomacy DCs and Changing Attitudes
Although there are many reasons you might care about a performance, the Perform action lays out one explicit outcome:
"... it might influence the DCs of subsequent Diplomacy checks against the observers - or even change their attitudes - if the GM sees fit.
The rules for Diplomacy describe attitudes.
Acrobatic Performer therefore allows you to use the Perform action with Acrobatics (instead of Performance), also allowing you to change the DCs of future Diplomacy checks and perhaps changing attitudes.
The Advanced GM screen contains information from the Game-master’s guide that the main GM screen doesn’t have.
Correct (a list is below).
The contents of the GM screens is as listed on the GM screen section section linked above.
Correct, and then some. The AoN screen has things that aren't on either of the physical ones. (A list is below)
Does the Advanced GM screen omit any information that is present in the basic GM screen?
Yes:
- Basic/Special Action list
- Skill Action List (lists actions each skill has and what level of proficiency is required)
- Hero Point usage
- Specific Skill DCs (such as the DC for identifying a magic item or recall knowledge)
- Turn Order and Icon Key
- Exploration Activities
How do the two advanced GM screens differ?
AFAIK content wise they are the same, but I don't own the portrait version so I can't validate that.
Exactly what AoN GM screen rules are omitted in which screens?
What's missing from each screen is in one of those lists already. The following things are on neither screen but are on AoN:
- Earn Income table
- Temperature table
- Weapon traits table (what each trait does)
Are there any other differences that define the sort of GM each screen is suited for?
The Advanced GM screen includes rules from the Gamemastery guide that the standard screen does not:
- Creature Numbers (for creating monsters)
- Hazard Numbers (for creating hazards)
- Victory Points (a subsystem)
- Reputation Points (another subsystem)
If you are using these systems on the fly, this will be very useful. If you are not, they are not useful at all. In the case of Creature and Hazard numbers, on the fly means "you are making up a creature or hazard in the middle of a session". If you are making a creature in your prep, this information doesn't need to be on the DM screen as you will have its final numbers already.
The standard GM screen covers things that are always useful, and especially for a newer DM are things you will be looking up frequently. Some of them get easier to remember later and if the list above of what's removed from the Advanced screen is things you already know anyway, then the Advanced screen will probably serve you well.
But if you are looking those things up frequently, the standard screen is going to be used more often as a reference.
Best Answer
In the Game Mastering chapter, on page 506 of the Core Rulebook we get this information:
It is still left somewhat to GM decision what to share, but the intention is that you can learn one piece of information with one check, or two on a critical success. About what this "piece of information" is we get two other examples in the player section, on page 239:
These are really close to mechanical details, and I imagine this could mean a reveal of an exact numerical descriptor, such as AC or resistance, depending on play style. In most cases something like "You know it has a high Fortitude save" might suffice, as whether it has +20 or +25 might not change your decisions at all. The rules seem silent on how exact the information should be.
Also relevant is what we can read on repeated attempts to get more information, also on page 506: