I had 4 custodian and 2 Lil' Bad Wolf in the past month. Never had a Netherspace Abyssal drop but I snapped one off AH for 100g (I think seller meant 10k or something but never got response from seller)
Drop rate is pure luck. It's like flipping a coin. Normally you'd get 50% head or tail but sometimes you can flip and get all tail 25 times in a row.
Keep grinding, and keep checking AH for dirt cheap pet.
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