Stealth

Ambushing

Creatures can successfully ambush others by meeting certain conditions. They must not be visible to the creatures they wish to ambush, creatures behind cover are still partially visible. They must not make any movements, if they do they need to to roll a Stealth Skill Roll. Creatures that meet these criteria while waiting in hiding in order to Ambush others are considered to have rolled a 15 on their Stealth Skill Roll(Ambushing creatures can still Actively Roll Stealth, they simply convert any roll lower than a 15 into a 15).

The Ambushing Creature or Creatures that have their weapons drawn and readied may use their Reaction(s) to Fire or Attack as if they had prepared a Ranged, Melee or Spell Attack to Trigger upon seeing their targets come into Range. Charge Attacks are Considered to be a Single Action and can thus be used as a Reaction.

Additionally, creatures that already have their weapons drawn and readied in these situations gain Advantage(or +2 if they already have Advantage) on their Reaction Attack Rolls and gain a Situational +2 to Initiative.

Standoffs

The traditional Standoff sees one or more characters with weapons already drawn, pitted against one or more adversaries that have not already drawn or readied their weapons. The threat of violence and the fact that the Initiator of the Standoff has a significant advantage are very clear in these situations and the narrator or the players can easily set up a standoff in the right conditions. Entrances and exits to buildings make for excellent Standoff locations as if there is no movement made by the Initiators and line of sight can not be established by the Defenders there is little to no chance of detection prior to the Initiation of the Standoff.

Essentially a Standoff is an Ambush(see Ambushing above) that is used to Negotiate and Intimidate rather than Obliterate.

The Creature or Creatures that have their weapons drawn and readied may use their Reaction(s) to Fire or Attack as if they had prepared a Ranged, Melee or Spell Attack to Trigger upon seeing any threatening movement(Rolling Initiative). Additionally, creatures that already have their weapons drawn and readied in these situations gain Advantage(or +2 if they already have Advantage) on their Reaction Attack Rolls and gain a Situational +2 to Initiative.

Surprise Actions

Until discovered creatures can use their actions, spells, abilities and attacks while utilizing a rotating turn order. Initiative is rolled once a stealthed creature has been discovered via a passive or active perception check.

Stealth Bonus

Certain weapons and abilities grant bonus damage on attacks made while stealthed. The value will be listed in the ability description or Item stat block. Many weapons are silent but creatures can alert nearby allies to danger if they are still conscious.

Detection

Creatures that feel safe in their environment do not actively roll perception checks and scan for danger. Creatures that are on watch roll one active perception check for each hour they are on watch.

Detection is not always a spectacular reveal and a particularly well stealthed creature may only leave evidence of their position rather than being discovered. For instance a creature might hear the sounds of a bumbling invisible creature and start investigating rather than rolling initiative.

A rolled stealth check made by a creature to avoid detection plus or minus any relevant modifiers is equal to the perception DC requirement to detect said creature. All creatures utilize sound, sight, smell and vibrations to detect other creatures. Most creatures' passive perception covers a 10 meter radius around them and will detect any stealthed creatures with a stealth check lower than their passive perception inside that radius. Whenever a stealthed creature generates a significant amount of sound, scent, light or vibration such as casting a spell or making an attack they must roll another stealth check with disadvantage to attempt to remain undetected. If any Stealthed intruder is detected all relevant creatures(including still stealthed Players Characters) Roll Initiative. Detection of all other Stealthed Creatures is done individually.

Stealth After Detection

Breaking line of sight allows a creature to make stealth checks in combat or after having been detected. However these stealth checks are always made with disadvantage and a creature cannot gain the benefit of a successful stealth check until no longer on the same tile where they broke line of sight. Creatures automatically detect non invisible creatures they have previously detected when they regain line of sight. Line of sight can only be blocked by an appropriately sized and opaque obstruction, structure or object.