This hefty chain is made from dark iron, its porous links grow or shrink adapting the creature it bounds. The chain works as a leash that deprives a creature from its will.

You can spend an action attaching the iron choker to a Huge or smaller creature's neck. If the creature is unwilling it must succeed on a Wisdom Saving Throw DC 15, if it succeeds the choker falls of with no effect. The creature can repeat its saving throw at the beginning of its turn, with advantage if it has taken damage since. On a fail it must follow your every command as long as you hold the chain. On a save no effect takes place, but the creature must repeat the saving throw until the choker is removed, which it can attempt as an action passing a Strenght Saving Throw DC 16. A charmed creature makes its saves with disadvantage. A willing or unconscious creature automatically fails its Saving Throws. 

For the effect to take place the chain must be held by its wielder on a free hand if the creature is of size Medium or smaller, on both hands if it is large, or be held by two creatures with both hands if it is Huge (if both wielders give different instructions nothing happens). If the wielding requirements aren't met at any given point the creature bound by the chains may repeat its Wisdom Saving Throw (DC 15), and keep repeating it at the beginning of each of its turns as long as the conditions aren't met. The creature may or may not be hostile towards the wielders.

If the bound creature takes damage it can choose to repeat its Wisdom Saving Throw (DC 15), with advantage if the wielder(s) or creatures friendly to at least one of them deals it. The bound creature if unwilling at first can attempt a Wisdom Saving Throw (DC 15) every 10 minutes as its will kicks in fighting the chain, with advantage if at any point it took damage from the wielder(s) or creatures friendly to them. A creature that willingly puts on the choker, even not knowing of its magical properties, must succeed on the Wisdom Saving Throw (DC 15) in order to remove it. Any creature that succeeds on its Wisdom Saving Throw must then succeed on the Strenght Saving Throw (DC 16) in order to remove the metal choker.

Once the bound creature sets free the wielder(s) are considered to be cursed, and can't willingly let go of their grip (even after death) for the next 24 hours or until they bind the choker to another creature. A remove curse spell ends this effect earlier.