Okay I too have some thoughts given that I've laddered a lot recently
Xatu S --> A+/A
Xatu has been sitting in S rank with people saying "why is this thing S" for ages, because in the current metagame, it really shouldn't be considered S rank. Xatu's main role on a team is hazard prevention, mind games, deterring your opponent from spamming hazards. To this extent, I believe Xatu performs this role at A+ or A grade standard. Reasons for this being:
-Still a reliable Garbodor/Roselia/Weezing check.
-Hard walls Ferroseed, can run great coverage moves like Giga Drain and Heat Wave, Rhydon and Ferroseed are increasingly common.
-Great vs Stall/Toxic stall tactics.
Other roles:
-Utility in Thunder Wave helps out balance teams and bulky offense teams.
-Calm Mind attacker (outclasses Mesprit and Mushy in the sense it doesn't get stopped by Toxic).
-Fighting check (very important).
However, in the state of the current metagame, Xatu cannot be considered S rank for a few reasons:
-Shiftry and Skuntank, Skuntank moreso, are decent Xatu checks. Xatu can U-Turn on Shiftry but is Pursuit trapped by Skuntank, as well as being destroyed by the occasional Crunch Skuntank. Not to mention Xatu's lack of options to hit Skuntank back.
-Common Stealth Rock users in NU right now like Rhydon, Piloswine, Torterra, Claydol, all scare Xatu from coming in and blocking rocks through fear of being OHKO'd. Rhydon, in my opinion, is so common right now that it makes Xatu just so risky, it's presence on a team is nullified by Rhydon's own presence as it fully stops Xatu performing it's main role in blocking hazards.
-Fighting types bring Knock Off, Colbur Xatu is limited by it's lack of residual recovery in leftovers.
-Rotom (standard) and Rotom (fan) are both increasingly common and just cause Xatu all sorts of trouble.
That brings me to my next nomination:
Rotom A- --> A
I was honestly surprised to see this guy sitting in A-, not sure about you guys. Rotom has two very niche sets that are both equally good and that's what makes it so powerful, it's roles on a team are not always obvious from team preview which makes playing around it quite sketchy early game and can seriously harm your team if not prepared for.
The scarf set:
-Brilliant revenge killer and speed control to beat offense teams.
-Can trick it's scarf and pass status to cripple stall teams.
-Great fighting check and spin blocker.
-You can't really argue with STAB Volt Switch
The wisphex set:
-Rhydon check
-Lanturn is not really an issue
-Easy to bluff being scarf!!!
-Destroys balance
-Archeops check too wow
-Hex is so powerful it's stupid with a spell tag ._.
-Check this calc:
252 SpA Spell Tag Rotom Hex (130 BP) vs. 40 HP / 216+ SpD Lanturn: 183-216 (45.6 - 53.8%) -- 94.1% chance to 2HKO after Leftovers recovery and burn damage
252 SpA Spell Tag Rotom Hex (130 BP) vs. 40 HP / 216+ SpD Lanturn: 183-216 (45.6 - 53.8%) -- guaranteed 2HKO after Stealth Rock, Leftovers recovery, and burn damage
This means with a toxic spike up, you are guaranteed to 2hko it, one of Rotom's biggest counters destroyed immediately!
-More STAB Volt Switching shenanigans on top of all this.
Seriously Rotom is just so freaking good and versatile right now.