What are the range and requirements of a Dismiss action?

Question

Using his sharp ear to guide himself, the little cat walked gently across the unstable roof of the inn to the window where the conversation was closer. Even with the window closed, it was clearly the refined voice of the Marquis's right hand. He was commanding two rough men, probably two quarrelsome mercenaries, to engage the noble soldier in a street fight, so they could later accuse him of starting such fight and ... Oh no! another cat is in the roof, and is approaching hostile!

Clare opened her eyes. She was in the ground floor of the inn, pretending to be a simple customer – I have to dismiss my poor familiar before the cats start a fight and alert the men that someone could be listening to them – but she can't even see her familiar from there.

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Some effects, spells and even some magic objects can be dismissed using an Action, a Bonus Action or other. But which range and requirements does the Dismiss action have?

• Lots of them (Dragon Wings, Disguise Self and others) have a range of 'Self', so the range of the Dismiss action doesn't seem to be a problem. But can you dismiss them being Prone, Restrained, Grappled or when you are trying to be discrete? Does the Dismiss Action have Verbal, Somatic or Material Components?

• Others, like Find Familiar or Mage Armor, create an effect that can be very far before ending. Do you have to see the effect to dismiss them? Is there any limit on the range?

• If the effect was created by a magic item by itself (not merely giving you the ability to cast a spell), like Instant Fortress, do you have to be in possession of, touching, or near the magic item to dismiss it?

• Extra: Is putting a familiar into a dimensional pocket is comparable with the Dismiss action?

Answer 1

In game terms there is no such thing as a "dismiss action". Spells and certain abilities may grant you actions specific to them, including letting you end an effect or send something away, but those possibilities are always spelled out in their description. Also, their limits are discussed in the particular description fully. If a condition or limit is not mentioned, it does not apply.

Without explicit wording to say otherwise these actions are unique and do not belong in any category. They are not "cast a spell" or "use an object" or any other. As they are not spells, they cannot require components. If you can take an appropriate action (you are not incapacitated for example), you can take them.

Spells cannot be always ended by the will of the caster. Such cases are always explicitly pointed out. Note, however, that you can end concentration anytime (PHB 203) and thus end a spell requiring it.

Answer 2

There is no Dismiss action.

Some game effects, frequently spells, can provide actions a character can take to interact with the effect. For example:

Find Familiar:

As an action, you can temporarily dismiss your familiar. It disappears into a pocket dimension where it awaits your summons. Alternatively, you can dismiss it forever. As an action while it is temporarily dismissed, you can cause it to reappear in any unoccupied space within 30 feet of you.

Channel Divinity: Turn Undead:

As an action, you present your holy symbol and speak a prayer censuring the undead.

Caltrops:

As an action, you can spread a single bag of caltrops to cover a 5-foot-square area.

Giant Spider:

Web (Recharge 5-6). Ranged Weapon Attack: +5 to hit, range 30 ft./60 ft., one creature. Hit: The target is restrained by webbing. As an action, the restrained target can make a DC 12 Strength check, bursting the webbing on a success.

There you have a spell, a class feature, a piece of equipment, and a monster attack all granting a character an action they can take. All of the rules for resolving those actions follow their definitions. There's no need for DM interpretation in these cases; the effects do what they say they do, and nothing more.

The various "dismiss" actions mentioned in the question are just examples of this general pattern. In most cases (find familiar, mage armor, disguise self, etc) there's nothing more to it than the spell specifying that the spellcaster can use their action to end the effect. Find familiar also defines an additional action that can be used while the familiar is dismissed.

As for Daern's Instant Fortress:

The cube rapidly grows into a fortress that remains until you use an action to speak the command word that dismisses it, which works only if the fortress is empty.

As long as you can speak, and you are the person who placed the fortress in the first place, you can dismiss the fortress with the command word. The item description doesn't limit the range of this effect, so there are no such limits.

Answer 3

In general, you cannot dismiss an effect unless it says you can.

If you can, the description of the dismissal is explicit about what type of action you need to use (action, bonus action, or reaction), if any. The dismissal is its own type of action; it does not use one of the 9 actions detailed in the PHB under "Actions in Combat".

Range is not an issue (unless the description makes it one) - range is only relevant when the spell is cast. See my answer to the Q&A "Does going outside of range or line of sight after casting a spell have any effect?".