Hey guys. I kinda made an account on this forum to ask a question since i've started to practice a bit of Yoga for my dancing in order to get more flexible and just because i love stretching. 
But anyways, i'm wondering if anyone here would know any specific stretch to achieve this kind of flexibility.
Thanks. 
Hello Fayte,
Welcome to the forum.
That’s quite an impressive pose you’re showing there! It is not an “official” yoga pose, though. Even master Iyengar does not show it in his Light on Yoga book. It looks like a combination of a backward bend (like bow pose), a twist (like trikonasana) and an arm balance (like peacock pose). Quite a bit of spine flexibility is needed as well as considerable arm strength and a sense of balance. Just look at those biceps!
Why would you like to learn this?
As a dancer you might like some of the more dynamic expressions of hatha yoga - like asthanga or power yoga. So go for it and let us know how your flexibility develops. You might discover some of the other riches of yoga in the process.
Namast
Fayte – I’m not confident that what this person is doing is smart to do. My physical edges are still certainly in less advanced asanas, so there might be something going on there that I don’t notice, but so far I’d bet folks who do this often enough will feel their body’s revenge by the time they’re 70. Or maybe the pic is not exactly what it seems – do you know if this is an ‘action shot’ or if this was held steadily for a few seconds? Is the airborne foot pressed against that wall?
But, just in case, I recommend going to a yoga class and paying attention to how the teacher teaches down dog, side plank, the pigeon-like hip stretches, and the twists. . . and since you mention waist flexibility in the title, I’ll counter that by offering that a smart twist is gradual through the entire length of the spine and definitely doesn’t contain itself just between hips and ribs.
Again, I don’t know if the yoga class will bring you closer to this configuration or closer to an understanding that you don’t want to inflict this on the one body that will last your lifetime. But either way, good luck.
The best way to do that move: Photoshop! :P. No It looks real and yes there are those among us who are hyperflexabile and double jointed but I agree with Techne. That the posture might not be very safe. I’m not sure what sort of dancing you doing (I’m going to hazard to guess break dancing?) But keep in mind also a pose done slowly and saftly on a mat is going to have a diffrent effect on the body than a pose that is jumped into.
I believe the best way to achieve the position illustrated in the linked photo would be to post the question on a contortionist forum. Asana is not contortionism, yoga is not asana, and neither yoga nor asana are about flexibility.
[QUOTE=InnerAthlete;20496] Asana is not contortionism, yoga is not asana, and neither yoga nor asana are about flexibility.[/QUOTE]
I think you are right. Asanas are not just physical exercises. They have biochemical, psycho-physiological and psycho-spiritual effects. They act at cellular level.
Scroll down to chapter Asanas in the classic Hatah Yoga Pradipika:
Oak333 the link to me is extremely useful , thanks from bottom of my heart