Dark Souls Remastered | Defeating the two Less Sanctuary Guardians on NG+1, getting Guardian Tail

It isn't worth it to kill these guys for the souls or the loot. You can get a Guardian Tail by shooting one of their tails off, but that doesn't require killing it. If you do kill one without getting the tail first, it won't drop. It's similar to the Gaping Dragon boss in the the Depths. If you chop off its tail, you get a Dragon King Greataxe.
https://youtu.be/83sQ7enosd4

On my first attempt killing both these Sanctuary Guardians, I get the Guardian Tail off the first and kill it, then the other kills me. I go back and kill them both and get no loot. You otherwise only get 6,000 souls off each one for NG+1.

Lesser Sanctuary Guardian
http://darksouls.wikidot.com/lesser-sanctuary-guardian

Guardian Tail
https://darksouls.wiki.fextralife.com/Guardian+Tail