Overwatch's Mercy has been nerfed in the game's latest PTR, not long after the hero's recent rework.
In the last major Overwatch patch both Mercy and D.Va were remodelled to help balance the game. Mercy's ultimate ability was changed from Resurrect to Valkyrie, a move which grants the support character amplified skills and the ability to fly, while Resurrect became a regular move, albeit with a 30-second cooldown and a smaller range.
Since the patch went live, Mercy's been the most popular support character because, let's be honest, she's super powerful. But Blizzard seems to think she might be over-powered and so is testing some changes on the PTR.
Mercy's Valkyrie ability no longer resets or lowers Resurrection's cooldown. Previously, when using Valkyrie, Mercy's Resurrection cooldown was reduced from 30 seconds to 10 seconds, allowing her to resurrect teammates in quick succession. However now, the cooldown remains the same and instead Valkyrie now doubles Resurrection's range.
The change is currently only being tested, so is subject to change. However, you can try it out on the Overwatch PTR on PC.