What he's done to get picked up in fantasy:
In this case it is more of what did Clint Hurdle do to make Melancon a trendy fantasy baseball pick up (in this case remove Jason Grilli from the closer role) on what is a "temporary basis", it doesn't hurt that he already has 10 saves to his name and a shiny 1.89 ERA & 0.78 WHIP.
What to expect going forward:
His ERA is somewhat lower due to an .211 opposing BABIP but even looking beyond that , he has pitched good enough this year (2.46 FIP/2.88 xFIP) to indicate that he can be reasonably expected to pitch strongly the rest of the season and enough of a track record to indicate that he is capable of handling the pressures of being the designated ninth-inning pitcher.
If he does continue to outperform his strong peripheral statistics, he will need to maintain a low line drive rate (16.9% this year versus 21.3% career total). Bottom line, Melancon is a solid pick up if you need help in the saves category for however long he holds onto the closing gig.
For being a pseudo wild-card contender (35-37 record and 3 1/2 games behind the last wild card spot) the Pirates seem to be doing better in having players that are getting picked up by several fantasy baseball owners (Charlie Morton was one of the trendy pick ups from yesterday).
Back in 2006, Melancon was a ninth round draft pick (albeit from the Yankees). While he has pitched elsewhere in his career (with the exception of 15 games), Melancon has thus far been successful in the context of ninth round picks in that years draft as the only player from that round with a higher career WAR is David Freese.
No matter how long he holds onto this closer role and how successful he is during this time, one thing for certain is that he's not going to get the all time saves lead for pitchers who went to the University of Arizona as that happens to be the same school that Trevor Hoffman went to.
All numbers, stats, etc. referenced found on either fangraphs.com or baseball-reference.com