Shadow Hopper

You can do this achievement when the daily Catch! is up OR any other day by asking Elder Anli for your serpent to play with (she will also give you the ball). You have to be revered to do it on the non-quest day, though.

Your biggest challenge will be finding an area in The Arboretum without a ton of other people and their own serpents, and getting lucky with some terrain geometry that doesn't bug out (your serpent can throw the ball "under" some of the terrain). The crowded problem is pretty much completely eliminated by requesting your pet on a day when the daily isn't up from Elder Anli. The corral area next to Elder Anli is nice and flat and makes a good starting point.

If you miss a catch and need to start over, you may have to click off the "Juggler" buff to be able to throw the ball again. Fortunately the counting system for the achievement seems a bit buggy and will not always reset when you miss a catch, so you can rethrow and work your way up to 25.

I was getting desperate about not getting the daily quest "Catch" when, quite by chance, I found out that you don't actually need it. Speak with Elder Anli and she will give you an option to play catch with a hatchling- not sure if a certain reputation is required: I might have either missed it before or the option was not there before I hit revered.

So do not worry too much- you will be able to do it even if your serpent grows up :-).

also the counter seems currently bugged so even if you drop the ball the number stays there- I hit 8 stacks then dropped the ball and then only needed to do the remaining 17 (and not 25 from the scratch). have fun!

Appears to be bugged. Dropped the ball after 18 [spell=110562] and started over. I was then granted the achievement after 7 stacks.