I don't know whether this will get deleted due to my general lack of experience compared to other players here, but I would still like to say I support a suspect test of all three Urshifu, Spectrier and Magearna.
Urshifu :- Wicked Blow is a broken move in itself. It doesn't matter that Landorus - T switched in. Wicked Blow doesn't care about it. Add in a choice band boost and you have a pretty broken move. I don't think as broken as Thousand Arrows, nor is Urshifu as broken as Zygarde, but still broken. Clefairy and Fini fear Poison Jab. I used to have Scarf Lele on my team to revenge kill it. But that's where the problem came. I have to sack something to bring it in. If the opponent predicts the switch, then Wicked Blow KO'es my Lele. Then I have to use High Jump Kick on my Cinderace, which takes Zen headbutt and Sucker Punch from his moveset (Pyro Ball, U turn and Gunk Shot are necessary on a Cinderace for me), meaning Toxapex walls it all day. Also, most Urshifu's are paired with Spectrier (another mon I will talk about later) which means High Jump Kick is not as safe as I would like. What I can derive from this is that Urshifu forces 50/50's that are (unfairly) in the favor of whoever is using Urshifu. I can't switch in, Urshifu kills whoever is in, I send in my revenge killer, Urshifu switches out to a counter to my revenge killer, double switch and Urshifu is in. (I know because I have used Urshifu this way many times, and have been on the recieving end as well). And Sucker Punch makes revenge killing all the more harder. The cost of sacking mon to bring Urshifu in always lesser than the cost of sacking a mon to bring his check in. Urshifu will KO whoever you send in on the switch. Which is why I would support a suspect test (even if I'm not sure I will be getting the reqs). All this and I didn't even mention Future Port support, which takes care of it's only reliable counter, Buzzwole.
Spectrier :- Probably the least broken mon out of the three in the spotlight. But broken, I feel, nonetheless. While I will admit that I have never been swept by it, I also admit that I was lurking the forums for month before stepping in to play SS OU, and anytime a threat list came up, these three were on the top of it. Which made me start building a team with a Spectrier check who doesn't die to Urshifu easily (Mandibuzz), but loses to specs Magearna. I feel these three have enough of a broken ring attached to them on their own, but paired together, they make life worse for innocent players. Spectrier's best sets to me are both Specs and Scarf. Scarf makes revenge killing more difficult(and if you run scarf, you should be smart enough to not stay in on a Bisharp who is obviously carrying Sucker Punch) while Specs dent even resists. And no one wants to switch in consistently on a specs boosted shadow ball if they are not immune to it. Heatran dies to Mud Shot and gives it a free +1, thanks to renamed Soul Heart. Blissey can switch in but has to use Shadow Ball to break subs and if he is Sub + Disable, congrats. Spectrier will set up both sub and wreck havoc from behind. Will - O - Wisp allows it to cripple some of it's physical checks. But the above mentioned Bisharp is a pretty good check as I always end up predicting a sub or WoW and go for Knock off instead of Sucker Punch, then conveniently Spectrier tries to attack and gets KO'ed by Sucker Punch. While I know that using our experience isn't a valid argument, this is just to show that Bisharp does check it. But it is threatened by a Will - O Wisp so your check is permanently crippled, and is an open invitation for Urshifu to switch in and wreck havoc. As I said, they are great on their own, but their combination is exponentially more threatening.
Magearna :- While I admitted on the SQSA thread just today that I don't always understand how the EV's of bulky mon works, this one I have used to the most success. More so than both Urshifu and Spectrier, and would strongly support it's suspect test. The only way I kill opposing Magearnas is to play like HO on my Balance team and quickly switching in to my Cinderace to scare it out or KO it (of course, it's after I sack a mon to find out whether it's spec or AV or Shift Gear). Magearna, is one mon who can be seen as a real troll mon because as soon as I lure a heatran with my Cinderace (Baiting a Banded Pyro ball but going for the High Jump Kick and KO'ing), Shift Gear + Calm Mind just runs rampant and plays with the feeling of many people. Outside of Unaware Clefable (which for some reason I am seeing a lot less of), no one seems to counter(or even revenge kill lol) this set after a Shift gear + few Calm Minds, thanks to - A) Resisting most priority and B) Having a weak but still reliable after a few Calm Mind recovery in Draining Kiss. Even at 30 - 35 %, it isn't KO'ed by a Grassy Glide from Banded Rillaboom (mine is 252Def/252SpD/4HP, Timid) and recovers good amount of health with Draining Kiss at +2, which isn't hard to get on a defensive build. Specs set is another set which can severely dent teams with boosted Fleur Cannon and slow pivot with Volt Switch. It has amazing bulk and arguably the best typing defensively. Weakness policy sets are also a good on Shift Gear + 3 Attack sets but I have played around it while using neutral hits at first then going for the super effective hit if I'm not sure that it will be OHKO. Assault Vest provides Mag with immense special bulk and you are better off not trying to attack it from the special side while Fleur Cannons are blasting holes. Overall, I feel Mag is the most broken mon out of the three.
I am sure these three will be tested. Pheromosa is gone. After these three are (hopefully) gone, the meta will be much more better I feel as some Pokemon that were completely overshadowed before will see some usage and more diverse teams will be seen. And I don't think this will lead to a slippery slope as the next best thing is Cinderace, which while great, is not broken in my opinion.
Hope my post wasn't repeating what others have said.
EDIT :- I know I said that the horse is the least problematic out of the the three, but it's still so stupid that I sweeped a team in the 1600's (it's somewhat low but still) when I held the wrong item. The team did have a dark resist and an Urshifu but still got destroyed. Funnier when we consider that my phone autocorrected Leftover as Level Ball, and I was still able to trap his Urshifu in Sucker Punch/Wicked Blow mind games and picked off the members one by one.