The ZenFone Pegasus 3s (written Zenfone飞马3s in Chinese) comes with a Sony IMX258 1/3.06-type 13MP 1.12-micron mid-range BSI Stacked CMOS image sensor and accompanied by a a 78.4-degree (~26.5mm equivalent focal length) f/2.0 aperture lens and on-sensor 0.2 sec phase-detection autofocus system. The IMX258 sensor is already found in many other mid-range smartphone, including among other, the Xiaomo Mi5s Plus, Sony Xperia XA, OnePlus X, Meizu M3E, Elephone P9000 Edge, Xiaomo Redmi Pro, BLU Vivo 6 and others.
The IMX258 sensor is capable of capturing very detailed images in daylight or in good ambient light, but it falls short in low-light, Thewhich is understandable considering its very small pixels. Having a dual-LED flash is nice for close-ups, but obviously doesn't have strong illumination to light up subjects in a distance. The colors that this sensor is capable of producing is really amazing, with very natural greens and reds.
The Sony IMX258 is also capable of 4K 30fps video recording, although according to the phone's spec, this phone doesn't support 4K video recording for some reason.
So overall it's a an average but I not bad offering considering the phone's price (1999 Chinese Yuan, approx. $288 USD) that can get the job done, but if you are an enthusiast photographer who also care about image quality and low-light performance, it might be better for you to look on some alternative as well. It's nice that the camera comes with a fast f/2.0 lens, compared to the OnePlus X and Xiaomi Mi5s Plus that comes with the same sensor unit, but has a slower f/2.2 aperture. I say that if you put on a camera phone with a sensor with relatively very small pixels, at least equip it with a very fast lens, so the camera will have less need to to push up the ISO and will overall elevate it's low-light performance.
I've read on the web that some people like the sensor's output performance in daylight, but if you look at the Sony IMX258 performance as a whole, I think it's quite lacking. I wouldn't mind having it in an entry-level phone, but in 2017, I would expect a new sensor with bigger pixels and one that can perform better in low-light and can produce better image quality and have higher dynamic range. The dynamic range of this sensor seems very low if I judge by the sample images taken with cameras that use this sensor. This is why shadows are less detailed. So my conclusion is that this sensor is really average, and has poor nighttime performance and this is why I categorized it in the 'Disadvantages' section.