GM EX Powers

The following are what are known as GM EX Powers. Essentially, if a GM sets the difficulty of a scenario higher than Normal (see V. GAME MASTER in the Release Document.txt), or if an enemy with the [Boss] tag appears in a scene, the GM will be granted a certain number of Fate Points. These Fate Points can be spent exactly like a PC can spend them, but these EX Powers allow a GM a wider variety of effects. Use them to enhance the difficulty of scenarios however you see fit--simply pay the Fate Point cost during the listed Timing, and apply the effects. Remember however that the goal of Log Horizon TRPG is to create a fun atmosphere. If your players are not comfortable with high difficulty in combat, you should rethink using these.

If an effect stipulates to treat it like an Other Status, this means that the effects cannot stack.

Scenario Actions
As a quick note, Scenario Actions do refer to actions undertaken through attributes such as Athletics or Perception. However, typically the actions are designed to be more specific to the scenario at hand, and often are tailored to the party's subclass, such that having an appropriate subclass can offer a bonus to the attempted roll. I've went ahead and translated three example Scenario Actions from the book's pre-made scenario. They apply specifically to a scene wherein the party must navigate through a forest.

The scene is set up like a literal board game, with 11 spaces arranged somewhat like an S-shape with a few branches. When a player makes this action, they move the party marker one space (if they're successful), and up to three spaces if they're really successful. The players never quite know in which direction they need to travel, and the spaces may contain 'Happenings', or events, such as fighting a Cave Spider, finding a locked treasure chest, or picking refreshing berries. They begin in the Start space, and must find their way to the Goal space.

Remember those Happenings? Well, if they hit a monster encounter like the Cave Spider, it's not a combat encounter so much as an abstracted scene of fighting. Afterwards, the players get +1 Exhaustion Counter, rather than making an Exhaustion Roll like they might otherwise do. At the end of the scene, whether the players have successfully found their way out or not, the players add their Exhaustion Counter to the Exhaustion Table: Stamina roll. So if they have 2 Exhaustion Counters, they roll 1d6+2. This action lets players remove counters.

Finally, a simple enough thing, an action that boosts another one.

In the end, Scenario Actions used in this way are somewhat like skill challenges in D&D games. So now you know what the use of the Increase Mission Difficulty EX Power is, and also how to design your own Scenario Actions!