Saw a post on page nine by
-Magic- about unranking Whimsicott and didn't really see any replies about it, so might as well post my thoughts.
Whimsicott
should remain D rank imo. Sure, it seems pretty bad, especially when you compare it to things like Tangrowth and Amoongus, and its nice set of resistances is kind of irrelevant when you see its crappy defense and special defense stats (basically all of its stats, tbh), but Whimsicott should be ranked as it has a defined niche in the metagame and is pretty good at what it does. Whimsicott's decent movepool and immunity to Dragon type makes it a decent pivot for balance teams that appreciate the speed control Whimsicott provides. Priority Encore is an extremely valuable thing to have, as it allows you to switch in pokemon setting up, such as Clef and Zard X, and lock them into their setup move, forcing them to switch out. From there, Whimsicott has several options on how to punish the switch, such as stun spore, knock off, or u-turn, all which result in an increase of momentum for the player.
Whimsicott's versatile moveset allows the player to prepare for certain threats to their team that they are weak to. For example, if a balance team is weak to stall and decides to add Whimsicott to their team for speed control and utility, Whimsicott can use a moveset containing Knock Off, Moonblast, Encore, and Stun Spore. STAB Moonblast allows Whimsicott to 2HKO Mega Sableye most of the time, which in turn forces it out from mega evolving, allowing an easier time for you to set up hazards. Furthermore, Knock Off really hurts stall's answers to Whimsicott, mainly Heatran, which really appreciates the passive recovery. Lastly, Encore prevents things like Clefable and Chansey from doing their job properly. Against balance teams, Whimsicott really shines as its speed control in Prankster Stun Spore is extremely useful. Being able to paralyze ground types (Landorus in particular) is pretty sweet, too. Against offense, Whimsicott's speed control is extremely useful, being able to cripple things like Mega Lopunny and Weavile with the correct prediction. Access to Momentum can act as a nice setup for a setup sweeper you have on your team, such as Zard X.
Regarding metagame shifts, I've seen no rises or drops that really affect Whimsicott's ranking that much. The presence of Volcanion is actually somewhat beneficial for Whimsicott, as it consequently raises the usage of Landorus, which Whimsicott has a pretty good matchup against. Sand is still pretty strong and with correct prediction Whimsicott can really help you gain momentum by forcing it out with Encore if it Sword Dances or Earthquakes and then punishing the switch. Garchomp is still extremely common and Whimsicott pretty much cockblocks most variants. Whimsicott is actually a decent check to the pretty common Keldeo, as if it switches into secret sword, it can force it out with encore and gain momentum with it's several options. Latios is still a strong pokemon in the metagame and is checked by Whimsicott due to the pressure of being Encored on a Defog or Draco Meteor. Mega Latias is a great pokemon still and Whimsicott acts a a great check.
So, yeah, Whimsicott should remain D rank do to possessing a pretty good niche in the current metagame.