Surprise is always checked by group, not by individual.
This check is rolled against a creature's (or group's) Surprise chance. This is listed in a stat block as SURPRISE x%.
If not indicated, this chance is 30% (01-33 on a d% indicates that you're surprised).
Always use the best (i.e. lowest) Surprise check value of any individual in the group for the group’s Surprise chance.
Some creatures are good at surprising others or can use items or skills to enhance their ability to surprise others. This is the modifier to an opponent's Surprise check. If not indicated, it is 0% (no modifier to the opponent's Surprise chance).
Always use the worst value of any individual in the group for the group’s Surprise chance.
The modifier is typically indicated as bonus although the value is SUBTRACTED from the opponents Surprise check. In general, a creature with a better surprise others capability must be, at a minimum, 90 feet in front of those without the ability for it to be functional (and even then, they are the only one rolling for surprise).
Roll a Surprise check (d%) for each group. Ignore the check result if a group cannot be surprised.
Subtract an opponent's surprise others modifier, if any, from your Surprise check.
If the result is under your group's Surprise chance, your group is surprised.
If surprised, the result indicates the number of segments (referred to as "Surprise Rounds") your group will be inactive. See the Surprise Flowchart above.
If the results indicate that one group can act while another group is inactive, the GM will run a Surprise Round.
Typically, surprise only exists only for a brief moment before full awareness sets in and a group can act.
Thus, surprise only exists for a few segments at best and usually just for one segment. Remember that a round is 1 minute and a segment is only 6 seconds. This means if you surprise a group of opponents, you have a tiny amount of time to do something before they react.
That said, anyone who is surprised is especially vulnerable due to the fact they are not fully aware of you.
Dexterity Reaction Adjustment. Individuals with a high Dexterity score will have the surprised condition for fewer segments during the surprise round. This does not mean that they can act, just that they do not have the surprised condition during certain surprise segments. Any individual with a penalty to Dexterity Reaction will extend surprise for their entire group, although only they will have the surprised condition during the extended segments.
Surprised Condition. During each surprise segment, a creature with the surprised condition can be targeted by attack actions. A creature with the surprised condition cannot take actions, including free attacks or immediate attacks so opponents can move past them or into melee and (in the next surprise segment, if any) attack with a melee weapon. See also Targeting a Creature without the Surprised Condition During a Surprise Round below.
Initiative. The GM will use the Combat Flowchart for each surprise segment where one group can act and another cannot. Any surprise segments where both groups are surprised are ignored. Initiative is automatically won by the group not surprised. Declarations must be made as normal.
Attack Actions. For the group that can act, each member can attack a surprised foe using one attack routine per surprise segment. It is important to note that melee can only be executed if an opponent is in range (and all movement, including that as part of a charge attack, consumes the normal amount of time).
If you target an opponent who is in the surprised group but who does not have the surprised condition due to a Dexterity Reaction bonus, the GM will inform you that your attack will happen during the normal combat round. Area attacks function normally.
Ambushes. If the GM determines a group has perfectly executed an ambush with missile weapons arrayed in optimal fashion, then extra attack routines may be granted based on the perceived level of optimization (up to a maximum of two extra missile attack routines available to the ambusher per surprise segment).
Innate Abilities. Only one magical innate ability can be completed during a Surprise Round no matter the number of segments available. A magical innate ability is a spell-like ability or an innate ability that functions as per a spell (duplicate or largely similar). Innate abilities that occur as part of an attack action including gaze attacks can occur each segment of surprise. Only one breath weapon attack can occur during a Surprise Round.
Spells. Only one spell (incantation or invocation from a magic item) can be completed during a Surprise Round no matter the number of segments available or casting time. If a spell has a casting time over that of the number of Surprise Segments available, the casting will continue into the first Combat Round and will be considered the caster's major action for that round (the casting time is the remaining time left to complete the spell).
All Other Actions. All other actions occur based on normal time required with each surprise segment treated as a normal segment during a typical combat round (and will continue into the first Combat Round if appropriate, using up the creature's action as ruled by the GM).
If you target an opponent who is in the surprised group with an ability but who does not have the surprised condition due to a Dexterity Reaction bonus, the GM will inform you that your attack will happen during the normal combat round. Area attacks function normally.
Example #1. The PCs encounter a group of goblins. Each side rolls a surprise check (d%). The PCs roll a 58 (+28 = Not surprised). The goblins roll an 18 (33-18 = 15 = 1 Surprise Segment). All of the goblins are surprised for one segment during the Surprise Round. The PCs, armed with bows, can attack normally (bow fire rate is 2 so two shots for each bow wielder) before the normal combat round begins.
Example #2. The PC's group, including a ranger and a thief with a 17 Dexterity, are investigating a series of caves. They carry lit torches and they're talking while exploring. A group of troglodytes wait camouflaged against the wall of the cave the PCs just entered and the GM determines they cannot be surprised. The GM (privately) rolls a Surprise check for the PCs and they roll a 28. Because a ranger is present, the group's Surprise is 17%. However, the troglodytes have a surprise others modifier of +34%. So the surprise check is (28 - 34) = -6. Thus 17 - -6 = 23 = 2 Surprise Segments. Thus, all PCs have the surprised condition, with the exception of the the thief who has a Dexterity Reaction Adj. of +2 versus surprise. Each trog can throw 2 javelins (one per segment) before the normal combat round begins. If any troglodyte targets the thief (who has no surprise segments due to her Dexterity), the attack will occur in the normal combat round (and any surprise segment attacks are lost for that troglodyte).