​The Phoenix Mercury can’t help themselves. They love a beguiling big three. Their latest foray came on the eve of Sunday’s trade deadline, acquiring two-time WNBA champion Kelsey Plum from the Los Angeles Sparks. Plum, a five-time All-Star, will slot in next to six-time All-Star Alyssa Thomas and five-time All-Star Kahleah Copper. The Sparks acquired second-year guard Monique Akoa Makani, a 2027 first-round pick and a 2028 second-round pick. It’s a pie-in-the-sky attempt by the Mercury, a 2025 WNBA Finals squad that woke up on Sunday a full six games out of the eighth and final postseason berth. At 11-19, they are 13 games back of the league-leading Lynx (24-6) with 14 games to play. Should the Mercury miss the playoffs, they would be the first to do so in the season immediately following a Finals appearance since the franchise did it in 2008. The fit for the Mercury to reach that final spot requires a PhD in mathematics. There is a clear stratification between the league’s top eight and bottom seven, leading to movement within the groups but likely not between them as the league barrels toward the World Cup break (Aug. 31-Sept. 17) and playoffs. That makes the deal a curious one — though it could work out — and throws the Sparks into another rebuilding-via-draft era. Mercury take big swing, big gamble Phoenix began its season with a bang, blasting the reigning champion Las Vegas Aces, 99-66, on the road in a Finals rematch. Everything since was a dud. During a season in which offense is booming, the Mercury took a step back. Their 104.7 offensive rating is only better than the Storm, Mystics and Sun — all of which are far younger teams that weren’t expected to challenge for a playoff spot. Losing Satou Sabally in free agency and not backfilling the production took its toll. Plum, assuming she is healthy after a lower leg injury kept her out since June 21, is an immediate improvement. It gives the team a big, a wing and guard playing at All-Star levels. Plum was named a reserve for last week’s showcase in Chicago, but could not play. Her spot was given to Copper; Copper and Thomas arguably missed the cut for their team’s first-half performance. The 2017 No. 1 overall pick and former NCAA Division I women’s scoring leader averaged a career-best 23.9 points per game in 12 appearances for Los Angeles this year. It ranks second behind A’ja Wilson (26.8 ppg) on an efficiency that rivals the Aces forward. Plum is shooting a career-high 52.7% overall on a career-high 15.7 attempts, largely as a result of finishing at the rim (85 FG% in the restricted area) and double the efficiency in the midrange (61.5 FG%). Each are marks in the 99th percentile of the league, per Her Hoop Stats. It’s the defensive drop that really hurt the Mercury after riding it four wins short of a title last year. That side of the ball isn’t going to take a dramatic leap by adding Plum and losing Akoa Makani, an elite perimeter defender the team leaned heavily upon in