Heh - I have a few pets, but I am proudest now of my full collection of farmed whelpings :-)
Have the Crimson Whelpling, Emerald Whelpling, Dark Whelpling and Azure Whelpling.
But the Emerald Whelpling was a real sod - I used to keep a mob count addon going until a year ago, and it reckoned I had killed 7,200 Adolescent and Dreaming Whelps with no drop (supposed 0.1% or 1 in 1000 drop off the Dreaming Whelps) and I have reguarly farmed for it since then, must be an absolute minimum of 9,000 kills.
And after almost 2 years of sporadic farming, it dropped for me 2 weeks ago

I just shouldn't get so obsessed!
P.S. Searched, but couldn't find how to make Emerald Whelpling an item link?