[RPG] What magic items are there to capture or restrain someone

There are two official optional rulesets for crafting

Both are optional and require that you work with your DM as to if they're an option and how they'd work. In either place that these rules appear, they are optional variants to the base rules.

Dungeon Master's Guide

The first official optional rules released appear in the Dungeon Master's Guide in chapter 6 as part of the "Downtime Activities" section:

Crafting a Magic Item

Magic items are the DM’s purview, so you decide how they fall into the party’s possession. As an option, you can allow player characters to craft magic items.

Within these rules, there are the following requirements:

• a formula that describes the construction of the item
• the character must also be a spellcaster with spell slots and must be able to cast any spells that the item can produce (and expends the relevant spell cost each day during crafting)
• the character must meet a level minimum determined by the item’s rarity
• a required gold and time cost to craft the item during downtime (consumable cost half as much as other magic items)

\begin{array}{c|c|c} \text{Rarity}&\text{Cost}&\text{Minimum Level}\\ \hline \text{Common}&\text{100 gp}&\text{3}\\ \text{Uncommon}&\text{500 gp}&\text{3}\\ \text{Rare}&\text{5,000 gp}&\text{6}\\ \text{Very Rare}&\text{50,000 gp}&\text{11}\\ \text{Legendary}&\text{500,000 gp}&\text{17}\\ \end{array}

Xanathar's Guide to Everything

An alternative ruleset is part of the optional variant to downtime as a whole (and one I personally think is more fleshed out) that appears in the supplement Xanathar's Guide to Everything in the "Downtime Revisited" section of chapter 2:

Crafting Magic Items. Creating a magic item requires more than just time, effort, and materials. It is a long-term process that involves one or more adventures to track down rare materials and the lore needed to create the item.

Within these rules, there are the following requirements:

• a formula for a magic item in order to create it
• an exotic material to complete it. This material can range from the skin of a yeti to a vial of water taken from a whirlpool on the Elemental Plane of Water. Finding that material should take place as part of an adventure. (the suggested challenge rating of the creature to face, though not necessarily harvest the material from, appears in the table below)
• whatever tool proficiency is appropriate, as for crafting a nonmagical object, or proficiency in the Arcana skill.
• a required gold and time cost to craft the item during downtime (consumable cost half as much as other magic items). Do note that downtime rules as a whole are revised when using the Xanathar's Guide to Everything rules

\begin{array}{c|c|c|c} \text{Rarity}&\text{Challenge Rating}&\text{Time}&\text{Cost}\\ \hline \text{Common}&\text{1-3}&\text{1 workweek}&\text{50 gp}\\ \text{Uncommon}&\text{4-8}&\text{2 workweeks}&\text{200 gp}\\ \text{Rare}&\text{9-12}&\text{10 workweeks}&\text{2,000 gp}\\ \text{Very Rare}&\text{13-18}&\text{25 workweeks}&\text{20,000 gp}\\ \text{Legendary}&\text{19+}&\text{50 workweeks}&\text{100,000 gp}\\ \end{array}

Simple enough...

Bead of Force: Creates a bubble of Force energy. You can roll it around like a hamster ball, and it only lasts for one minute...but anything inside only weighs 1 pound. Bear in mind, it deals some damage when it first goes off...so don't hit fragile targets with it. It is also expended on use.

Bowl of Commanding Water Elementals: Bit of an odd choice here, but Water Elementals have a native Grapple ability (Whelm) that they can use to constrain enemies

Cube of Force (attuned): Use to create a Cage Match if you get close to an enemy. For one minute, they are trapped within 15 feet of you.

Dimensional Shackles: Practically a Must if you intend to capture a spellcaster, as this is the most reliable way to block teleportation long-term.

Eyes of Charming (attuned): Charm Person is a great way to get people to willingly come with you.

Helm of Telepathy (attuned): Suggestion feature is also great for getting people to surrender and come along.

Immovable Rod: Put someone on their stomach, press one of these into the center of their back and push the button. They'll have a devil of a time getting their hands around to de-activate the rod, and they aren't getting up while it is pinning them.

Iron Bands of Bilarro: Fling a ball of metal at a target, and it restrains them. DC 20 Str check (once per day) to break free of it.

Iron Flask: Only works on creatures from a different plane of existence than the one you are on...but it works great for that purpose.

Mirror of Life Trapping: Not super portable, it's a 4' tall mirror, but...save or be indefinitely locked inside of one of 12 extradimensional cells. No escape clause except for someone letting you out. Keep this thing's command word a very closely guarded secret so no one can use it against you.

Rod of Rulership (attuned): As long as you haven't attacked this person, you can Charm them into thinking you are their leader...and then order them to come with you. It'll wear off in 8 hours, but by then...it'll be too late.

Rope of Entanglement: A rope that you can sic on people, and it attempts to tie them up.

Staff of Charming (Attuned): Again, magic people into coming along willingly

Tentacle Rod (Attuned): Doesn't exactly restrain, but it slows, gives them disadvantage on Dex saves, and seriously interferes with their action economy. They'll have a hard time resisting you in that state.

Wand of Binding (Attuned): Lets you cast Hold Person or Hold Monster...paralyzing targets makes them very easy to capture.

Wand of Paralysis (Attuned): Basically the same thing as a Wand of Binding

Wand of Polymorph (Attuned): Snails are remarkably easy to capture.

Wand of Web (Attuned): Fire restraints at your targets