» Sun Jan 17, 2016 8:40 pm
In order to farm a Legendary, you need to save outside of the cell the Legendary spawns in. In the Wasteland, this is difficult to do, but if you save outside of a building, you can pull it off that way. The idea is to have one save outside the door, and one save inside. You go in, kill the legendary enemy, then check its loot. If the base item for the Legendary isn't something you're interested in (Synth Armor when you want a Shotgun, for example), reload the save outside. If the item is correct, but the effect isn't, load the save inside to get a different effect.
It is worth noting, though, that the information I've seen says Quicksave outside, then rely on the Autosave that is created inside. I don't know how strict these requirements are; does doing a hard save inside lock something in that the auto-save doesn't? And of corse, there's the issue that opening your pip-boy also creates an auto-save, so you wouldn't be able to actually pull it up without possibly ruining the farm.
Also, I should note: I've never farmed a legendary myself, so all my info is second-hand.