Occasionally a party may maneuver themselves so adeptly that their enemy is completely caught off guard. In this case, the GM may grant the party advantage on Initiative, or in extreme cases, they may not need to roll Initiative at all—the GM can allow each Hero to start with all 3 actions!
If the heroes are surprised, they may have to roll with disadvantage. Or, in extreme cases, the heroes may automatically start combat with only 1 action, or the monsters may all go first.
A Note on Surprise Merely being hidden or punching first is not sufficient to gain Surprise! If an enemy is on guard or at all aware of your presence, they cannot be surprised.