In his last six starts, Greinke's ERA is 0.43. If you go back one more start, you get his sublime 15 strikeout performance against Cleveland, in which he allowed a *terrible* two runs. In his last seven starts, his ERA is 0.72.
Pitching for a horrible team, in front of a horrible defense, against one of the toughest stretches of the schedule, he's turned it on.
I know ERA is a problematic stat, but it's damn near impossible to have a sub 0.50 ERA if you aren't, well, awesome.