Surprise (game mechanic)

 Surprised is a special condition that can affect creatures during the first round of combat.

Overview

When one side of a combat encounter is unaware of the other side, they may be Surprised. A Surprised creature cannot take any Actions or Reactions for one combat round. Characters with the  Alert feat, the  Feral Instinct feature or specific items (such as the Elixir of Vigilance) cannot be Surprised.

Certain combat encounters, especially ones that occur after an in-game cutscene, are set to always surprise the party. These can usually be countered by utilizing the aforementioned features or else conditions such as  Invisible or hiding in heavily obscured areas with spells such as  Darkness before triggering them.

How to Surprise Enemies

The key to surprising enemies is line of sight: they must have a clear line of sight to the character surprising them. If they do not, then they will begin searching for that character and will NOT be surprised once they find them and begin combat.

This can make it challenging and counter-intuitive to successfully surprise a group of enemies. Precautions such as the following may aid in the process:

1. Use  Hide to put the ENTIRE party into stealth, including pets.
2. Ungroup the party, including pets, then select one party member as the ambusher and move them into position to trigger the surprise.
3. Keep the other party members and pets some distance away while the ambusher approaches the enemy from outside their vision cones. If they cross a vision cone in a  Clear Area then they will instantly be spotted, but if they are  Lightly Obscured or  Heavily Obscured then they must succeed a  Stealth roll against the enemy's  Perception check. On a successful roll the enemies will not notice the character, but on a failed roll they will initiate combat without being surprised.
4. The ambusher MUST initiate combat from within line of sight of the enemy. If they do, then the enemy should be surprised. However, if they are out of line of sight then the enemies will begin searching for the party member and will NOT be surprised once they find them and begin combat.
5. The way you initiate combat matters. Here are some key points (but the testing has not been exhaustive):
   1. Melee attacks always work.
   2. Ranged attacks done on melee range always work.
   3. Spell attack rules are either bugged or complicated. Spell attacks work nearly always for melee range and a bit less often for non-melee range. The following examples demonstrate the discrepancies:
      1.  Eldritch Blast (attack roll) works both for melee and non-melee range.
      2.  Witch Bolt (attack roll) works for melee but not for non-melee range.
      3.  Fireball (Dexterty save) works for melee but not for non-melee range.
      4.  Fear (Wisdom save) works both for melee and non-melee range.
      5.  Magic Missile (no attack roll) works neither for melee nor for non-melee range.
   4. If the attack type (melee, ranged, spell) works, it doesn't matter whether it hits or misses.
   5. Grenades don't work, even if you hit the enemy directly.
   6. For  Ambushing enemies, every type of attack, even grenades, work, as long as enemies have not spotted your party. This is true even if you failed the  Perception check and attack the currently empty location where the enemy will turn out to be.
6. Once the enemy is surprised, the rest of the party can be moved into position to join the fight. They will be drawn into the fight once they either enter an enemy's vision cone or attack them.

If a character's Stealth is high enough then enemies will sometimes fail to notice them even as their allies are being attacked and killed from a distance. This can even work with Area of Effect spells such as  Fireball as long as the party member casting it remains hidden. The enemies will run around in a desperate search for the party member but be unable to find them. This can be accomplished with a high Dexterity score, Proficiency and Expertise in stealth, Advantage in dexterity or stealth checks, and certain spells and abilities such as  Pass Without Trace.

Triggering Surprised from Invisibility

The most reliable way to surprise an enemy is to become Invisible and attack them. This invisibility can come from any source (e.g Potion of Invisibility,  Invisibility,  Greater Invisibility, or Shadow of Menzoberranzan). The Quasit and Imp pets will also work, as will  Wild Shape: Panther.

List of Surprise encounters

Act 1

• Sneaking into the Overgrown Ruins Refectory will leave Andorn surprised.
• Interacting with certain caskets in the cave inside the Apothecary's Cellar will cause an Agile Guardian to burst out and surprise the party.
• Attacking the bloated hyenas along the Risen Road will leave them Surprised.
• In the Underdark, approaching the Petrified Battlefield will initiate combat with a Spectator, triggering a cutscene which leaves the party surprised.
• Approaching the Underdark Beach will trigger a conversation with a Duergar. If attacked immediately, the whole Duergar party will be left surprised. If Gekh Coal is called and he turns hostile, the player's party will be surprised instead.
• In the Grymforge, attacking the 3 Mimics will always surprise the party when interacting with them in their disguised form. Attacking them from range will start the battle without being surprised.
• Magma Mephits will surprise the party if they approach the mithral vein closest to the Adamantine Forge.

Act 2

• In the Shadow-Cursed Lands, 3 separate encounters with Blights can surprise the party if they get too close to them.
• In Moonrise Towers, attacking the Mimic will always surprise the party when interacting with them in their disguised form. Attacking them from range will start the battle without being surprised.

Act 3

• At the end of "Dribbles'" performance at the Circus of the Last Days, the party will be left surprised unless the ambush is noticed through passive Perception checks, in which case the ambushers will be surprised instead.
• In Entharl's basement, for The High Harper quest, a group of doppelgangers posing as Harpers can be spoken to. A combination of dialogue checks and choices can lead to either the party or the ambushers being surprised.