Like the aforementioned Heatran, opposing Rotom-Washes can be pretty annoying, as it can easily cripple Toxicroak and Jirachi, due to it outspeeding the former at max speed and taking pittance from the latter's attacks (except for Heart Stamp against frailer builds), and it can wear either one down with WoW. It also deals supereffective damage to everything else on the team, and is therefore very tricky to switch into for this team. Slowbro and Starmie are similar but can be taken down by your own Rotom-Wash though. I'd suggest something like Serperior over maybe Lando-T and rocks on Diancie perhaps? Serperior can be really useful, trust me. Leaf Storm boosts, 113 base speed, boosting on Bullshitdoze and Sticky Web, and Substitute and/or Glare. It's good. That team already covers a lot of things too.