Welington Castillo played on three teams last year, but the third one was the charm. In his first 45 games with the Diamondbacks, "Beef Welington" (yes I really want this nickname to stick) went yard 13 times. That pace was obviously unsustainable, but it was impressive nonetheless. That run he had has him poised to be the starting catcher in Arizona now though, and it is tantalizing to see what he can do with a full season's worth of at-bats.
Don't expect anything in terms of batting average or OBP as power is really the main source of his fantasy value. The good news there is that he's going to be playing in a ballpark that's very conducive to this. The lineup around him would have been better in Chicago, but he was blocked there by Miguel Montero. Hitting in a lineup with Paul Goldschmidt isn't exactly a bad alternative either though. He's not in the top tier of catchers, but he has nice power upside and could be a top 15 backstop this season.