Time to make a bad opinion I will regret later when ladder stops spamming sun, but from my testing and my facing of Mr Wake, I have to feel that he has been misjudged because he is not broken right now but likely will be later. right now every team is using wake+hatt (I was using eject scream tail and I saw vert using just lefties scream tail for it), it means you always have to play a guessing game with it while also it not being that amazing vs teams with good prio/pex/amoong and slowking. This is due to it using +speed proto for the amount of offense going around rn. My preferred set and (most likely the set that might actually make it broken when people start using other playstyles) is the modest specs Tera water(in sun)or dragon (outside sun) set that can effortlessly throttle defensive teams while being decent vs offense with a nice speed tier and decent bulk. While this is fairly speculative (though I have been using it a bit), I found it amazing right now on ladder with the offensive teams being spammed and there will be a natural return to more balanced/bulkier playstyles that this set obviously takes advantage off, and I don’t see any way for these teams to answer this without running specific sets with Tera’s like Tera fairy clod/Tera water blissey, etc. basically speed boosting is good but not broken, spa boosting specs either modest/timid creates a unhealthy mu vs bulkier teams where they can’t reasonably handle it without running specific niche checks
List of Checks/Counters to Walking Wake 
Water Absorb Clod with Tera Fairy will win the 1v1 against Walking Wake while providing great utility. I made a post about it just above this if you want to read more.
Slowking has the combination of Regenerator and Slack Off that makes it very hard to break, the only problem is it cannot do much back to Wake. Otherwise, it is a very solid pivot that should reliably counter Walking Wake.
Blissey is in the same situation as Slowking, but it provides different utility. Also, it can win the 1v1 against Walking Wake much more easily than Slowking.
Sp. Def. Toxapex serves a similar role to Slowking as a Regenerator pivot. It can also spread Toxic, posing a threat to Wake.
These Water-types are all decent checks with 2 being immune to Water moves, but a good prediction will cause trouble. Azumarill resists all 3 moves, but it has no reliable recovery; not to mention, sun-boosted Specs Hydro Steam 2HKOs normal Azu sets. Gastrodon is a worse Clod imo since it cannot tank as well on the special side and misses out on Toxic. Vaporeon cannot damage Wake and has to rely on Wish spam & stalling out Draco Meteors. They all are viable picks though, and they offer utility outside of the Wake matchup.
These Fairy-types are immune to Walking Wake's Draco Meteor and can pressure back with Fairy moves while possessing solid enough Sp. Def. to deal with a Water move as well as reliable recovery. Scream Tail outspeeds Wake, both Scream Tail and Sylveon can pass Wishes, both Sylveon and Florges can set up with Calm Mind, and Florges can take advantage of sun spam with the boost in healing from Synthesis.
These Steel-types resist Draco Meteor, have good enough bulk to potentially tank Water moves, tank a Flamethrower, and will be useful outside of Wake matchups. Gholdengo has Recover, and Kingambit can Sucker Punch to deal solid damage.
These Grass-types are quite specially bulky and can kind of check Wake. Both Wo-Chien and Toedscruel can Leech Seed, they both tank Flamethrower easily, and both provide Knock Off support. Toed can also Rapid Spin, set up Spikes, and Spore if need be. Yes, I'm a big Toed enthusiast.
On the off-chance that Wake lost its Choice Specs or is running another item, Cryogonal can actually beat Wake while not being deadweight on the team. Freeze-Dry just barely OHKOs offensive Wake with 8 EVs in Sp. Atk.; it provides Rapid Spin and Haze support; it has reliable recovery; it is a Ground immunity. Very niche but very cool.
Chansey is Blissey but worse. It serves as a check rather than a counter because hazard stacking and/or getting Eviolite Knock'd Off removes its ability to wall reliably. Still an option I guess, so I'll toss it in here.
Dragapult can use either Draco Meteor or Dragon Darts.
Roaring Moon can use Scale Shot, Outrage, or CB Dragon Claw. It will outspeed any Wake variant in the sun with the typical CB set.
Iron Valiant can use Moonblast or CB Spirit Break.
Dragonite can Tera Normal, tank a hit, Dragon Dance up, and outspeed. It can also just Extreme Speed to pick up the kill.
Choice Scarf or Focus Sash Garchomp can use Draco Meteor, Outrage, or Dragon Claw (Wake must be chipped).
Choice Scarf Hydreigon can use Draco Meteor.
Choice Scarf or Focus Sash Glimmora can use Tera Fairy Dazzling Gleam (OHKOs Offensive Wake 37.5% of the time).
Maushold just outspeeds Wake, and it can either go for Population Bomb or use Tidy Up on the switch.
hippowdon can use stealth rock, phase with whirlwind which annoys offense like crazy (especially shed tail scrubs), and sand is amazing for residuals, breaking sashes, multiscale etc. hippowdon can even pp stall a lot garganacl's salt cures which is amazing in longer games
tyranitar is also a fine 'mon. outside of setting up rocks and sand, it can also pressure great tusk on the switch with ice beam and spread paralysis. the typing is also decent since it can check non-band dragapult, certain volcarona sets, skeledirge, and iron moth.
