Is The Bordelands 2 DLC Plot Related?

It's a mix of both, there are two upgrade packs which increse the level cap and add some small extra stuff to the game, there are 5 different skin packs for each character (including the DLC ones). There are two character DLCs, Gaige comes with the premium pack (which also includes a golden key and the golden guns pack) and Krieg comes with the Psycho pack. There is the collector's edition pack that comes with skins and a unique grenade and the slaughter dome which is a wave based challenge DLC.

Captain Scarlett and her Pirate's Booty, Mr. torgue's Campaign of Carnage, Sir Hammerlock's Big Game Hunt and Tiny Tina's Assault on Dragon Keep are the four main story DLC's, and they all take place in the order they are listed. After that there are 5 Holiday themed Headhunter Packs, each of which are small story based DLC's with exclusive skins and heads you get for beating the main boss at the end of each.

to get most of the DLC for a decent price, pick up Borderlands 2 Game of the Year Edition if you're playing on PS3 or Xbox 360. It comes with both characters, the four main story DLC's, the collector's edition pack, the slaughter pit and the first Level upgrade pack.

If you get the Borderland's Handsome Collection on Xbox One or PS4, you get ALL of the DLC