I'm on my 2nd playthrough of Borderlands and I have only 30 guardian kills towards the 'What is that Thing?' guardian kill challenge.
I've noticed that at the end portion of the game, you kill a bunch of those Sera Guardians, but they don't bump your guardian kill count for the challenge.
According to the wiki:
A Sera Guardian is an aerial form of Guardian, pink and greyish-green
in colour, that levitates high in the air during combat.
I understand that killing Boz Scaggs doesn't count against your Skag kill count, but these things are Guardians.
So, why don't they count?
Best Answer
Not quite sure. However, if you still wish to gain the accomplishment, then a great place to go is the Eridian Promontory, which is close to the end of the game. Interestingly enough, the Guardian kills in this area do not seem to count, yet the achievement does show up after 50 kills. So, this is probably an overlooked glitch by developers.