Rules Reference: Difficulties and Degrees of Success and Failure

DIFFICULTIES
Mutants & Masterminds can be broken down into a series of tasks the heroes must perform, from piecing together clues about a villain’s latest scheme to blasting said villain through a wall and disarming his doomsday device in the nick of time. It’s up to the Gamemaster to assign the difficulty of these and numerous other tasks in the game and to determine the outcome of the heroes’ efforts. Checks are made against a difficulty class or DC, a number set by the GM, which your check must equal or exceed to achieve success. So for a task with a DC of 15 you must roll a check total of 15 or greater to succeed. In some cases, the results of a check vary based on how much higher or lower the result is than the DC, known as its degree of success or failure.

THE 55% RULE
The chance of an average character (with a modifier of 0) succeeding at an average task (DC 10) is just over 50% (55% to be exact). So any time you have to have an average character do something of average difficulty they have roughly a 55% chance of succeeding in it. If you want to know what bonus is required to have a 55% chance of succeeding at a particular task, just subtract 10 from the DC. So a DC 25 action (a formidable task) requires a bonus of +15 in order to have a 55% or average chance of success (on a roll of 10 or higher). Keep in mind that this chance of success on a task allows a character to automatically succeed at that task as a routine check (see below). A 55% chance also allows a player to spend a hero point to automatically succeed, since a hero point ensures
a die roll of at least 11.

CIRCUMSTANCE MODIFIERS
If the situation is in the character’s favor, that’s good for a +2 bonus on a check. If it’s against the character, that’s a –2 penalty. If things are particularly good or bad, up the circumstance modifier to +/–5.

ROUTINE CHECKS
A check normally represents performing a task under a certain amount of pressure, in the midst of the furious action of super-heroic adventure. When the situation is less demanding, you can achieve more reliable results. Under routine circumstances—when you are not under any pressure—instead of rolling the die for the check, calculate your result as if you had rolled a 10. This ensures
success for average (DC 10) tasks with a modifier of +0 or more. More capable characters (with higher bonuses) can succeed on more difficult checks on a routine basis: a +10 bonus, for example, means a routine check total of 20, able to succeed at DC 20 tasks on a routine basis, and achieve three degrees of success on average (DC 10) tasks on a routine basis. If a character’s routine check result is not up to a task, the player still has the option to roll the die, since the task is by definition not routine for that character.