Can a Will-o'-Wisp be put inside a bag of holding?

Question

My players were fighting their way through a swamp and they were fighting some will-o-wisps.

The fighter had a fun idea to put one of them inside the bag of holding. Since it was at the end of the encounter, I thought it would be cool to let them pocket the wisp.

I'd like to know if, by RAW, it would be possible to do that (I already let them do that either way). Since the wisp can't be grappled, I don't know if such action would be possible by using force, but the way the player worded the action made me imagine they'd use the bag like a net to capture the wisp.

Also, would the wisp just pass through the bag to get out or wait until there was an opening?

Answer 1

The Wisp has Incorporeal Movement

The will-o’-wisp can move through other creatures and Objects as if they were Difficult Terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

So it doesn't seem like the wisp can be kept in the bag against its will - it can just pass through the walls of the bag. What happens then...is best left to a separate question. ('What happens when a creature with Incorporeal Movement leaves the confines of an Extradimensional Space?')

Wisps - you can't live with them (Consume Life), and you can't put them in a sack (Incorporeal Movement)!

Not grappling

While there is no RAW way to put the wisp (or another Tiny creature) in the bag of holding (or another bag), I would not suggest using the grappling mechanic to achieve this. As written, the Grappled condition assumes an active attacker holding the grappled creature in place by using their hand (the condition ends when the grappler is incapacitated or the creature is moved beyond the grappler's reach - neither of which seem to apply to capturing something in a bag which could be closed and left unattended).

An Improvised weapon

An Improvised Weapon:

includes any object you can wield in one or two hands...Often, an improvised weapon is similar to an actual weapon and can be treated as such...

Using the bag is closest to using a net, since a net is used to capture not damage, and a target hit by a net is restrained

A restrained creature’s speed becomes 0, and it can’t benefit from any bonus to its speed. Attack Rolls against the creature have advantage, and the creature’s Attack Rolls have disadvantage. The creature has disadvantage on Dexterity Saving Throws.

These conditions reasonably represent the condition of being confined inside the bag.

It is the GM's call how similar the bag would be to a net, and which of a net's properties would be used when attacking with a bag as an improvised weapon. Personally, I would:

Retain the restrained condition on a hit. However, note that a bag cannot be seen through, so the advantage to hit the restrained creature would likely be offset by disadvantage for attacking an unseen opponent.

Remove the proficiency bonus to attack. Unlike a net (which is a martial weapon), creatures will not have a proficiency in attacking with the bag.

Retain the limit on one Attack per turn. Along with not being proficient, creatures should not be able to use a bag to make Extra Attacks.

Possibly make the bag a melee, finesse weapon. Nets are ranged weapon, but a bag is not made to be thrown, so should be counted as a melee weapon. Depending on technique, either strength or dexterity might improve your chances of getting something into the bag. However, note that one always has disadvantage to attack with a net (since you are either attacking at long range or at 5 feet or less with a ranged weapon). Bags should not be better than nets, so I would either rule that attacks with a bag are at disadvantage or that you cannot apply an ability score bonus to the to-hit roll.

A net can be used on size Large and smaller creatures. I would restrict the bag to size tiny creatures.

Answer 2

How good is a Warlock's aim? This might work

It is arguable that if...

1. A Warlock PC is using Eldritch Blast
2. The Repelling Blast invocation is chosen (on a hit it moves target 10')
3. The Warlock is directly opposite the player holding the bag open, aligned on the will-o-wisp.

... then a will-o-wisp could be knocked back 10 feet away from the Warlock and into the bag of holding...IFF they line it up "just right."

Gust of wind might be similarly used in an attempt to 'bag' a Will-o-Wisp. Druid, Sorcerer, etc. but the rogue holding the bag needs to make that strength save.

A line of strong wind 60 feet long and 10 feet wide blasts from you in a direction you choose for the spell's duration. Each creature that starts its turn in the line must succeed on a Strength saving throw or be pushed 15 feet away from you in a direction following the line.

How could this work?

Some stuff from the Stat Block

Will-o'-Wisp / Tiny Undead / Speed 0 ft., fly 50 ft. (hover)
Resistances: Acid, Cold, Fire, Necrotic, Thunder; Bludgeoning, Piercing, and Slashing from Nonmagical Attacks Damage Immunities Lightning, Poison Condition
Immunities: Exhaustion, Grappled, Paralyzed, Poisoned, Prone, Restrained, Unconscious
Senses Darkvision 120 ft., Passive Perception 12
Languages The languages it knew in life
Proficiency Bonus +2
Ephemeral. The will-o'-wisp can't wear or carry anything.
Incorporeal Movement. The will-o'-wisp can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Is it small enough to fit into the Bag of Holding?

Per the DMG, the opening is 2 feet in diameter.

Creature Size

Each creature takes up a different amount of space. The Size Categories table shows how much space a creature of a particular size controls in combat. Objects sometimes use the same size categories.

Size Categories

Size | Space
Tiny | 2 1/2 by 2 1/2 ft.
Small | 5 by 5 ft.
Medium | 5 by 5 ft.

Space

A creature's space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions. A typical Medium creature isn't 5 feet wide, for example, but it does control a space that wide. If a Medium hobgoblin stands in a 5‐foot-wide doorway, other creatures can't get through unless the hobgoblin lets them.

From this we can infer that the Will-o-Wisp is small enough to fit into a 2' diameter opening.

Mechanically, this is still up to the DM.

The rogue holding the bag might need to make a check (Dexterity? Sleight of Hand?) to position the bag correctly so that the Warlock has the chance to knock it into the bag. (Other ability checks could be used, that's an example).

Once inside the extradimensional space/bag, Will-o-Wisp is probably trapped.

While this calls for another ruling, a regular sack would not work since the Will-o-Wisp has the ability to move through solid objects.
But inside of the bag of holding, it is now in an extra dimensional space. Bag of holding isn't like other objects.

How would I rule this?

Give it a try. If you can make your initiative actions, the rogue, the bag, and warlock (or other spell caster using Gust of Wind) all line up, and make the Sleight of Hand check, you succeed.

But when you next reach into the bag of holding, don't forget that there's a Will-o-Wisp in there.

Shock. Melee Spell Attack: +4 to hit, reach 5 ft., one creature. Hit: 9 (2d8) lightning damage.

Answer 3

You can put it in, but it might not stick

In summary: you can finagle the will-o'-wisp into the bag, but whether you can keep it in there, or whether it can escape or destroy the bag from the inside will be up to your DM. Either of the two would make the effort a bad idea in most circumstances.

Can you get it in?

The Will-o'-Wisp is immune to the grappled condition, so you cannot grapple it to put it in the bag, but you still could push it in. To paraphrase from that answer

There are no general rules for incorporeal creatures that make them entirely immune to physical interactions, the Will-o'-Wisp only has resistance to physical damage, so it clearly can be interacted with.

The next question is if the bag allows this. You clearly can put creatures into the bag, as the bag states:

Breathing creatures inside the bag can survive up to a number of minutes equal to 10 divided by the number of creatures (minimum 1 minute), after which time they begin to suffocate.

The bag has no special rules stipulations for putting something into the bag, so that works like with any old bag. If the bag is open, you should be able to push the will-o'-wisp in, or maybe can try and snatch it with the opened bag.

Can you keep it in?

The interior of the bag is an extradimensional space. That means there is no other side of the interior of the bag. So there is nowhere to go to for the will-o'wisp, once it is in the bag, other than maybe the lid, even though it could move through walls. Can it get back out through the lid?

The bag states that

Retrieving an item from the bag requires an action.

The overwhelming consensus is that you cannot open a bag of holding from the inside. Even though the will-o'-wisp can fly, and is incorporeal so it could move through the lid without opening it, the answer's interpretation of the sentence quoted above is that the only way to get something out of the bag is to retrieve it.

I don't agree: that you need an action to retrieve an item does not logically imply that a creature cannot leave it actively. You are not retrieving this creature when it does that, so the requirement to use your external action does not apply, and the wisp could just move out through the closed lid. But I think that there are such different viewpoints means this is best left to your DM do decide.

Can it destroy the bag?

Furthermore, there is no conclusion if you can damage the bag from the inside, because the bag's text does not talk about that either. It merely says

If the bag is overloaded, pierced, or torn, it ruptures and is destroyed, and its contents are scattered in the Astral Plane.

You could rule that because the inside is an extradimensional space this does not work, but earlier editions of D&D allowed destroying it from the inside. So that again is up to the DM.

In addition, the will-o'-wisp has no attack that would allow it to pierce or tear the bag, it can only shock it with its shock attack. So rules as written it cannot destroy the bag from the inside, even if that is generally possible, and it again would be a DM call if burning a hole with electricity would work to rupture the bag, as this upvoted answer postulates. If it would, the will-o'wisp could escape to the astral plane, destroying your bag and getting rid of all your stuff while doing so.