You can find the Excalibastard weapon in the
Stanton's Liver area.
As you arrive in the area, head left and jump across rocks to get to it.
Excalibastard is a legendary weapon floating above a stone.
Where to go in Stanton's Liverhttps://goo.gl/images/V5ktqPART THOU BADASS ENOUGH?
In order to pull the weapon from the stone, you must have a minimum Badass rank of 2,500.
If you are attempting
The Challenger trophy, then you would likely hit this number somewhere in the mid level 30's.
You can only pull the weapon once per character, which carries over between multiple playthroughs. So if you pull it at level 30 on NVHM, you
cannot pull it later in TVHM or UVHM.
The weapon's level will scale with you, but max's out at the current mode's level cap. From what I've read online, the recommendation is to wait until level 50 in TVHM for this weapon.
Here is the Wikia page regarding the weaponhttp://borderlands.wikia.com/wiki/Excalibastard