Addressed below are several of the common situations and issues that you'll invariably need to handle during the game.

Skill DCs

It is up to you, as the GM, to determine the DCs of the various skill checks the players will attempt during play. Many of the skill descriptions include guidance on typical DCs for skill checks, but there may be times when you need to come up with a DC on your own. If a skill check does not have a predetermined DC, or if a player wants to attempt a task that is not covered in a skill's description, use the following guidelines. A challenging DC for a skill check is equal to 15 + 1-1/2 x the CR of the encounter or the PCs' Average Party Level (APL). For an easier check, you might reduce the DC by 5, while increasing the DC by 5 makes for a more difficult check. Changing the DC by 10 or more makes for either a trivial check with little chance of failure or a prohibitively high check with little chance of success, so be cautious when adjusting skill check DCs!

Rolling and Fudging

Player cheating can ruin a game, but as a GM, you may sometimes find yourself in situations where cheating might actually improve the game. We prefer to call this “fudging” rather than cheating, and while you should try to avoid it when you can, you are the law in your game and shouldn't feel bound by the dice. A GM should be impartial and fair, and in theory, that's what random dice results help support. At the same time, you're trying to create a compelling story, and if fudging a given roll makes a scene more fun and satisfying for the players in the end—go for it! It's no good if a single random roll of the dice would result in a premature end to your campaign or in a character's death when the player did everything right. However, be wary of using fudging to nullify players' achievements. Remember that you're playing with the group, not against it. Maybe you didn't expect the players to take down your villain so quickly, but as long as they had fun, who cares?

An easy way to avoid getting called out on your fudging is to make your dice rolls behind a GM screen, so that players can't see the results. But don't worry overmuch about being “caught.” As the GM, your responsibility is to the experience, not the dice. But if you elect to roll your dice in the open, you still shouldn't show a die roll that would give a player knowledge that their character wouldn't have, such as a saving throw for a disease a character doesn't know she's been exposed to.

In addition to not being bound by die rolls, don't feel tied to the predetermined plot of an encounter or the rules as written. Feel free to adjust the events or interpret the rules creatively, especially in cases where you as the GM made a poor assumption to begin with. For example, you might design an encounter where a pack of demons have invaded a space station through a planar rift, only to realize too late that none of the PCs have good-aligned weapons and thus deal very little damage. In this case, it's okay to “cheat” and say these particular demons are hurt by normal weapons, or have a chaplain of Iomedae show up at the last moment to bless the PCs' weapons. As long as you can keep such ad-hoc developments to a minimum, these on-the-spot adjustments can even enhance the game—perhaps the church of Iomedae now demands a favor from the PCs, sparking a new adventure!

GM Fiat

Debates over rules inevitably drag a game down and should be put to rest as quickly as possible. As the GM, you set the law of your game, and your interpretation of the rules is the one that matters most. When complications regarding rules interpretations occur, listen to the players involved and strive to be fair, but don't feel like you need to convince them. If the rule in question isn't one you're familiar with, you can go with a player's interpretation, perhaps with the caveat that you'll read up on the rule after the game and make an official ruling going forward from the next session. Alternatively, you can simply rule that something works in a way that helps the story move on.

One handy tool to keep on hand is the GM fiat: simply give a player a +2 bonus or a -2 penalty to a die roll if no one at the table is precisely sure how a situation might be handled by the rules. For example, a character who attempts to trip a robot in a room where the floor is magnetized could take a -2 penalty to his attempt, at your discretion, since the magnetic pull exerted by the floor anchors the construct.

Player Character Death

Eventually, through bad luck or bad tactics, a player character is going to die, or else suffer some similarly permanent fate such as petrification or being shot into deep space at relativistic speeds. A player character's death doesn't need to be a terrible experience. In fact, going out in a blaze of glory can become a dramatic highlight for the player and the group as a whole!

When a character dies, try to resolve the current conflict or combat as quickly as possible. Once that's handled, take the player aside for a moment and find out whether she'd prefer for the group to try to save her character or simply create a new one.

You aren't required to let a dead character return to life. Sometimes dead is dead—and a horror-themed game often benefits from a sense of danger—but it's nice to take a player's feelings into account. If it's possible for the party to get a character raised or reincarnated, don't delay it with additional encounters; just gloss over the return to civilization so you can get the player back into the game as quickly as possible. If you'd rather treat the situation as the seed for a side quest, consider offering to let the PC play an established NPC for the rest of the session so she isn't bored. A PC death is a great time to end the session, since you can then handle unresolved issues out of game and get the player back in the action by the start of the next session.

If the player of a dead character instead prefers to move on to a new character, consider the NPC option above to keep her entertained for the rest of the session, or let her create her new character there at the table. Once the player's new character is done, let the other players take a 5-minute break while you step aside to talk to the player, learn about her new character, and work out a way to introduce the new party member quickly.

One other thing that PC death can do is bloat the surviving characters' treasure. If a party simply splits up or sells a dead PC's gear, the group can become obscenely overgeared for its level. Thus, it's usually easier to simply assume that the dead PC's personal gear (though not necessarily important story items belonging to the group) is destroyed, lost, or otherwise goes away.

Difficult Players

As with any group activity, sometimes you'll run into a troublemaker. Don't be shy about politely and firmly asking a player to alter his behavior if he's being inappropriate, antagonistic, or otherwise annoying—and don't accept “But I'm just acting how my character would!” as an excuse. If a player (or character) is negatively impacting the rest of the group's experience and won't change his behavior when asked, it's your duty as the Game Master to tell him to leave.

Campaign Journal

Having a record of each session's events can help you remember details and keep a sense of continuity. Consider taking notes during a game or getting a player who's excited about such things to write up a campaign journal summarizing each adventure. These can also be distributed to remind players where you left off.

Ending the Campaign

Starfinder goes up to 20th level, but that doesn't mean your campaign has to. The most important thing in a campaign is to end it at a point that's satisfying for the story, such as when a major storyline wraps up or after a climactic battle with a longtime foe. After each significant adventure arc, discuss as a group whether you'd rather continue with these characters or start something entirely new. Some people like to play many short adventures with different characters, while others like to run the same campaign for years. There's no wrong answer!