Starting with your request, I worked out how Floatzel and Muk would work together - by itself, Muk addresses most of the Electric- and Grass-types that check Floatzel, with very few exceptions. For example, Rotom-F, Zebstrika, Cacturne, Yache Leafeon all check standard Floatzel, but all fail to beat Muk 1 on 1 in most cases. To add to this, Muk can use most defensive answers to Floatzel as setup fodder (ex. Tangela, Quilladin, Lumineon, etc.), and by removing bulky Grass-types and Water immune Pokemon, Floatzel is able to clean much more effectively late-game. In return, Floatzel checks a large portion of the Ground-, Rock-, and Steel-types that Muk either can't touch at all or needs a few Curse boosts to work its way around. For example, popular checks or counters that are used to address CroMuk like Golem, Gabite, Krokorok, Probopass, etc. are all OHKOed by Floatzel, so the two complement each other well. Muk's EV spread is superior to the standard 252 / 4 / 252 set I see commonly used. Firstly, 12 Spe EVs let it click Rest on uninvested base 50s, while 248 HP and 8 Def let Muk live through one CB Frustration from Stoutland after SR (and the remainder is allocated toward Muk's Special Defense):
252+ Atk Choice Band Stoutland Return vs.
248 HP / 8 Def Muk: 306-361 (74 - 87.4%) --
guaranteed 2HKO after Stealth Rock and Black Sludge recovery
(without 8 EVs in Def): 252+ Atk Choice Band Stoutland Return vs.
252 HP / 4 Def Muk: 307-363 (74.1 - 87.6%) --
6.3% chance to OHKO after Stealth Rock
From there, I immediately sprang for a Golem counter, as that's currently one of Muk's most common checks in the meta (especially CB variants). Physically defensive Vibrava survives everything from Golem except for CB Explosion or Ganlon / Yache Natural Gift, while simultaneously preventing your Mawile, Floatzel, and Mr. Mime from being worn down too badly by entry hazards. A slow U-Turn brings Mr. Mime and Floatzel in for free, which is important in allowing Mr. Mime to wallbreak, as well as to let Floatzel scout out which Pokemon the opponent will use to counter it, so that you know which coverage move to lock into on the subsequent turns you bring in Floatzel. Vibrava can switch into Eviolite Monferno (but not SD LO variants) for the team, as well as Rapidash (especially Drill Run Rapidash), Metang, Stunfisk, RP Relicanth, Crustle, and Camerupt (but if you predict Camerupt to lock into HP Ice, switch to Chinchou instead). It also checks Muk
lacking Ice Punch (with CB Gunk Shot only dealing 38% maximum), as well as Arbok before either of these Poison-types have setup with Curse or Coil, respectively. Dropping its Speed IV by one point is something really simple but effective that you can do to gain momentum against other Vibrava users, as shown in the second replay above.
Even though Muk handles Electric-types well, it can't prevent them from gaining momentum and pivoting into a Muk check. That, and while Vibrava is immune to Volt Switch, it cannot switch into Electric-types given most of them normally use Ice coverage anyway. So, needing a hardier Volt stop of some kind to wall threats like Zebstrika, Raichu, Electabuzz, Rotom-S, Rotom-F, as well as other threats that would otherwise hamper the team's effectiveness, like Swanna, Pelipper, Regice, and specially offensive LO Floatzel, I added standard Chinchou. It forms a triple momentum core with Vibrava and Mawile, and slowpivoting is again useful in bringing in Mr. Mime to wallbreak and creating setup opportunities for Muk (as well as free turns of Black Sludge / Leftovers recovery for Muk / Mawile, respectively), especially given that most of Chinchou's natural switch-ins are Grass-types. In most cases, Chinchou can simply click Volt Switch on a predicted Leafeon or Cacturne switch-in for example, and immediatly pivot to Mawile or Muk for a free Knock Off, Stealth Rock, or Curse. Chinchou is protected perfectly from Rotom-F's TrickScarf by its teammates, namely, by Muk's Sticky Hold and by Choice Scarf Floatzel, so it shouldn't ever be losing its Eviolite (unless you come across something like Knock Off Raichu).
Next, the team needed SR, a Normal resist for threats like Stoutland and Dodrio, and Knock Off to weaken threats like Metang and Bronzor for Mr. Mime, so defensive Mawile was an easy pick. It can check Cacturne in a pinch, if necessary, and it'll act as your main answer to Leafeon before you have to resort to Muk for beating that (+2 Double-Edge can potentially break Muk, so Mawile should be your first line of defense against SD Leafeon). Optionally, Mawile can use full Defense and forgo the added Speed here, while trading Leftovers for Shed Shell, so opposing teams that rely on Probopass trapping for Normal-types will never be able to break past Mawile.
While Mawile is formidable as a Normal resist, it doesn't cover specially offensive Normal-types like Chatot at all. So, Soundproof Mr. Mime was added to compensate for this. Psychic-types like Mr. Mime are useful for luring or checking Steel-types outright (other examples of this include
Knock Off / Shadow Ball Kadabra and Specs Grumpig), and so Muk's need for Steel-types to be removed prior to setup is satisfied by Specs Mr. Mime - as I said above, it beats every Steel-type, except for +2 Pawniard and Klang with multiple Shift Gear boosts. Additionally, Specs Psyshock really throws annoying specially defensive walls and tanks for a loop, like Regice, specially defensive Clefairy, Chinchou, Audino, and more importantly, it is powerful enough to OHKO CroMuk without prior chip damage. Focus Blast is also very important in beating SpDef BU Ursaring and SpDef SD Bouffalant, so Healing Wish and Trick aren't necessary here. With the aforementioned Pokemon being mauled by Specs Mime, specially offensive Floatzel can easily clean up without having to worry about hitting multiple Focus Blasts late-game.
Finally, with deciding to use a more offensive variant of Mr. Mime to support Muk more effectively, Floatzel became my Choice Scarf user here by default. Floatzel's 4th move slot was dictated by what the rest of the team needed. It didn't really require HP Electric for Swanna or Pelipper, as Chinchou already addresses those competently; Baton Pass was already used by Mawile, and so the most viable last slot for this team was Switcheroo. Switcheroo is incredibly useful in improving your matchup against both stall by preventing walls like Audino from recovering, as well as slower setup sweepers like Duosion and CM Clefairy. Scarf Floatzel is also nice for its ability to outspeed and either OHKO or 2HKO every viable Choice Scarf user in the tier, just save for the Simis, Rapidash, and the rare Scarf Raichu / Electabuzz:
252+ SpA Floatzel Focus Blast vs. 0 HP / 0 SpD Rotom-Frost: 204-240 (84.6 - 99.5%) -- guaranteed OHKO after Stealth Rock
252+ SpA Floatzel Hydro Pump vs. 0 HP / 0 SpD Mr. Mime: 127-150 (57.4 - 67.8%) -- guaranteed 2HKO
252+ SpA Floatzel Ice Beam vs. 0 HP / 4 SpD Ninjask: 278-328 (105.7 - 124.7%) -- guaranteed OHKO
252+ SpA Floatzel Ice Beam vs. 0 HP / 4 SpD Chatot: 316-372 (107.8 - 126.9%) -- guaranteed OHKO
252+ SpA Floatzel Ice Beam vs. 0 HP / 4 SpD Leafeon: 228-270 (84.1 - 99.6%) -- 75% chance to OHKO after Stealth Rock
252+ SpA Floatzel Focus Blast vs. 0 HP / 0 SpD Sawsbuck: 288-340 (95.6 - 112.9%) -- 75% chance to OHKO
252+ SpA Floatzel Ice Beam vs. 0 HP / 4 SpD Dodrio: 244-288 (93.4 - 110.3%) -- 62.5% chance to OHKO
To conclude, this team is quite bulky and has a switch-in for the majority of the meta. In fact, it plays very similarly to stall, in that you'll be playing each Pokemon very conservatively up until it's time for Mr. Mime to break, Muk to sweep, or Floatzel to clean. This team's success also relies on Mr. Mime breaking successfully, as well as Vibrava and Chinchou keeping their Eviolites in tact, so try not to play with those too recklessly and scout for Knock Off first with Muk and Mawile before sending those two in. Anyway, I hope you enjoy!
