Successfully toss 10 rings onto Dubenko the Darkmoon Turtle in one session of the Ring Toss.
Rewards: Darkmoon Ring-Flinger
I found another way which i found easier to complete this. Basically i waited till the turtle was close left or right that will give you a secure shot! Video guide for proof :P https://www.youtube.com/watch?v=GQgFJfH3CM4
Achievement demo; http://www.youtube.com/watch?v=NduUADYsMFk
For those who don't want to watch the YT video, here's the trick: Dubenko always returns to the exact same spot. Wait until he begins moving back to that spot, then toss the ring. (Do not try to squeeze in two at once. It won't work. Be the tortoise, not the hare.)
That's what I did. Just remember that to include casting and travel time for the ring, or it will end up landing where the turtle was.