One more Build 10136 previously unknown feature here!! It seems ability to play GIF files natively comes with Windows 10 Mobile Build 10136. Not sure whether it was possible with earlier Windows 10 Mobile builds but it seems Windows Phone 8.1 was not able to handle GIF images natively. Not only GIFs appear in the “Photos” app now, but animations also play when you open the GIF image by tapping on them. You can also share the GIFs via mail and messaging and also play GIFs received via mail and messaging.
One cool trick that you may or may not know. When you open an image, video or GIF in Photos on Build 10136, you can just slide up to see the file details.
Thanks Sheik Althaf for asking.