What's the best way to combat Deo-D? (and why isn't this thing being suspected yet?)
Unfortunately, Deoxys-D is a really, really hard Pokemon to beat. If it's carrying Mental Herb, you can't stop it with Taunt, making it very annoying. Its bulk and Speed also guarantee that it can easily get up one layer and survive even extremely powerful super effective attacks. One way is to use Magic Coat, however, it's users are quite obvious, so Deoxys-D can easily switch out or Seismic Toss if it's carrying it. Another option is Magic Bounce. However, as you may know, Espeon and Xatu are pretty shit in OU now adays. However, I do remember awhile ago I ran a pretty fun Espeon set to counter DeoSharp; it was Focus Sash with Hidden Power Fighting and Shadow Ball, the former OHKO'd Bisharp while the latter did the most to Deoxys-D (though admittedly it was pretty bad outside of those match-ups, and even then it didn't always preform its job.
Honestly, Deoxys-D is almost guaranteed to get up at least one layer of hazards if he's running Mental Herb. My advise to run a hazards clearer; either run Excadrill, and if they carry Aegislash, to use Iron Head on the predicted switch to pop their Balloon, or run Latios with Hidden Power Fighting to OHKO Bisharp (since most Bisharp's on higher ladder tend to Pursuit) Overall, though, I think the main reason they're waiting on Suspect Testing Deoxys-D is because of the current Suspect Test now. However, I would not be surprised if you see it come up soon as Suspect, mainly do to the way it's been able to absolutely dominate the ladder.