In the SL cinematic, Sylvanas defeat Bolvar using chains. But, as soon she removes his helm, the chains disappear.(why?)
When Anduin was kidnapped, he was held by chains.
In the “Beyond the Veil” cinematic, The Jailer was held by chains too.
Maybe the chains only affect creatures with the taint of Shadowlands. Maybe there is something wrong with Anduin?
The chains are symbolic as well as literal.
Each link of the chain is an event, one event leading to the next, and with each successive event, the chain grows longer, it’s power to restrain and imprison made stronger. This isn’t even just in the sense of evil either, though it’s easy to make that comparison.
The very way the Shadowlands function means that we’re all forging chains throughout our lives, and the Arbiter simply determines to which afterlife they bind us.
Seems like it’s just the Jailor’s powers, a one of his signature abilities, if you will. I’m sure when we fight him, there will be chains all over the place.
Read this and immediately thought of Robert and Jacob Marley from Muppets Christmas Carol.
Have another to add to you and debunk your questioning.
The Val’kyr with Nathanos uses those same chains to try to lock Tyrande and the player character durinh the Night warrior questline.
Unconfirmed but those chains probably are what got thrall, baine, jaina and so on.
The chains seem to be roughly the analog to the “Jailer/Maw Covenant Ability”. As to what they exactly do we do not know (other than what chains normally do). There is an argument they repress supernatural abilities on top of physically restraining you. They seem to of restrained Jaina from using magic to escape her bindings, as well as kept Anduin from calling on the Light. Even from a physical perspective they were robust enough to keep Thrall contained as well a Baine… and the Tauren are nothing but muscle, so that is no easy feat.
As to why Sylvanas let Bolvar go? My best guess is it was a show of utter contempt for him. After the helm was destroyed she did not even see him as worth the effort of containing anymore, and Team Rocketed her way off into the Maw.