Seven runs - twice on heroic, five times on normal - and the pet dropped once.
Didn't get any pet from Yogg or LK.

I did seven runs through all three instances. Here is the outcome: Ulduar (25 man) 0x Magma Rageling 1x Ironbound Proto-Whelp 3x Runeforged Servitor 3x Sanctum Cub 1x Winter Rageling 2x Snaplasher 1x G0-R41-ON Ultratonk 0x Creeping Tentacle ToC (twice on heroic, five times on normal) 2x Dreadmaw 1x ...

I always liked the striders - they are so deliacte and pretty
So here's my little family:
PS. I'm on EU-Draenor. I already have Brightpaw and Hatespark the Tiny.

Big, BIG thanks to Et resurrexit legend for allowing us - pets hoarders - to get that little bastard!
Deathwatch Hatchling became the 715th pet in my collection!

I would like to especially thank Neolarva for putting the info here and Katrina for letting me in!

Thank you!

I spent some time yesterday, doing pet battles on my alt in order to get the achi and level up the alt at the same time (I was very proud of myself when I got the idea). All in all I got to 331/500 and just got very excited with the news. Description of the achievement in the game still says 500 pet...