The 2017 Yankees were a lot of fun, but 2017 Dellin Betances was not. Sure, he had a 2.87 ERA, but his wildness (I mean, the man was literally walking more than six batters per nine) and unreliability, especially in the later months of the season, led Joe Girardi to banish him from the circle of trust in the playoffs. Coming into the 2018 season, it was a total mystery whether we would see Good Dellin or Bad Dellin for most of the time.
Two months into the season, it's still too early to tell whether the Betances of old is back or is still lost.