https://esports.yahoo.com/overwatch-patch-notes-competitive-character-170000549.html
Patch video with Blizz designer
Mercy rework
Said Zen's ult is 300 hp per second instead of 200, moves twice as fast in ult, more shields (but not specified how much).
With Mercy you can move while ulting so she isn't a sitting duck that dies but she now builds ult slower. Apparently increasing damage boost power too.