step up, snap ya back
Whiscash faces some stiff competition for the role of bulky Water-type in the NU metagame. Its main competition, Wailord, sports similar defensive capabilities (in fact, they shake out to be almost identical) but also higher offensive stats and has access to two coveted moves in Roar and Self-Destruct. Whiscash, on the other hand, has what is possibly the best typing in the game and access to STAB Earthquake. However, despite just how good the Water/Ground typing is, the 4x weakness to Grass is what really lowers Whiscash's standing in the tier, as Grass is a popular coverage type on wallbreakers since there are many Pokemon that share Whiscash's unfortunate 4x weakness. If you can cover Whiscash's abhorration of the green stuff it'll pull its weight in any match.
name: Physically Defensive
move 1: Earthquake
move 2: Toxic
move 3: Ice Beam / Rest
move 4: Protect / Sleep Talk
evs: 252 HP / 252 Def / 4 SpD
With maximum Defense investment, Whiscash is physcially bulky enough to avoid a 2HKO from Choice Band Pidgeot and Hitmonchan, giving it an immediate niche in the tier. Physically defensive Whiscash vies for a team slot with Relicanth and Wailord, but there are a couple of things that make Whiscash worth using over both. While Relicanth resists Normal- and Flying-type attacks, and Wailord is a better Fire-type check by being less susceptible to Grass-type attacks and has Roar, Whiscash has an easier time offensively beating back Hitmonchan, resists Rock and is immune to Electric, and more easily takes on special attackers like Pikachu and Haunter (assuming they lack Grass-type coverage). Earthquake and Ice Beam have very good coverage together, and Toxic cripples most of the Pokemon that aren't too threatened by both. If you have a cleric on your team or need Whiscash to have greater longevity, RestTalk is an option in the last slot and allows Whiscash to absorb status for the team, but this also makes Whiscash a bit more susceptible to dangerous attackers like Substitute Pidgeot.
[ADDITIONAL SET COMMENTS]
A more balanced EV spread can be used to turn Whiscash into a more of a blanket check and try to make the most of Whiscash's set of resistances. With a spread of 252 HP / 140 Def / 112 SpD and a Sassy nature, Whiscash is still physically bulky enough to avoid a 2HKO from Choice Band Murkrow's Drill Peck and specially bulky enough to just barely survive a Fire Blast followed by a Hidden Power Grass from maximum Special Attack Flareon. Surf and a Bold nature can be run over Earthquake, but STAB Earthquake is a major selling point to using Whiscash over its competition.
Spikes expose Whiscash to a number of 2HKOes it can normally avoid, such as against Choice Band Kingler, Piloswine, and Pidgeot, making Rapid Spin support from Hitmonchan highly valued to get the most out of Whiscash. In the same vein, Spikes support of your own will allow Whiscash to nab some KOes it can otherwise miss out on, such as a OHKO on Pupitar and a 2HKO on Choice Band Hitmonchan. Roselia is the best Spiker to pair with Whiscash as it completely covers Whiscash's Grass-type weakness and in return Whiscash deals with a large majority of the physical attackers that give Roselia trouble.
name: Choice Band
move 1: Earthquake
move 2: Hidden Power Rock
move 3: Double-Edge
move 4: Surf
item: Choice Band
evs: 208 HP / 252 Atk / 44 Spe
This set is a far more offensive approach to Whiscash and really makes use of Whiscash's stellar typing and access to STAB Earthquake. Earthquake + Hidden Power Rock is amazing coverage, and Double-Edge and Surf round out the set almost perfectly. While Whiscash lags behind in power behind Piloswine and Graveler as a Choice Band user with STAB Earthquake, Whiscash makes up for it with its far better typing and ability to beat Hitmonchan and other threats such as Wailord and Dewgong one-on-one.
[ADDITIONAL SET COMMENTS]
Another big advantage that Whiscash has as a Choice Band user over its competition is its decent Speed stat, allowing it to allocate more EVs into its bulk. With just 44 Speed EVs, Whiscash outspeeds minimum Speed Chimecho and Flareon and everything below, including most other Choice Band users, giving it a leg up on slower defensive teams. Naughty is the nature chosen so as to not weaken Surf's power, and lowering Whiscash's Special Defense is of lesser consequence in the long run. If Surf doesn't suit your taste on this set, Hidden Power Bug or Hidden Power Ghost can be used instead, with Rock Slide then taking over Hidden Power Rock. Hidden Power Bug is Whiscash's best move for Bellossom and other Grass-types, while Hidden Power Ghost nails Haunter and Chimecho.
Spikes support is appreciated as this set is a bit unexpected and will inevitably force a lot of switches, thusly making it easier to nab some KOs Whiscash would otherwise miss out on. Roselia makes a naturally good partner to Whiscash as it covers its horrid Grass-type weakness. Flareon is also a stellar partner and can pass Wishes to Whiscash to keep it healthy over the match. Another offensive teammate to clean up, such as Dragon Dance Pupitar and Bulk Up Vigoroth, is needed to make use of the holes Whiscash is going to punch in the opponent's team.
name: Substitute Stallbreaker
move 1: Substitute
move 2: Earthquake
move 3: Surf
move 4: Ice Beam / Toxic / Hidden Power Grass
evs: 172 HP / 148 Atk / 144 SpA / 44 Spe
This set merges Whiscash's offensive and defensive potential to mold it into a deadly stallbreaker when used correctly. Whiscash's typing is perfectly suited to counteract the most common stall and defensive archetypes in the tier, with only other bulky Water-types standing in Whiscash's way of total team decimation. With the moves and EV spread given, Whiscash can create 101 HP Substitutes, giving it a totally free set up against standard physically defensive Sableye, and proceed to cleanly 2HKO with Surf. Roselia, Flareon, and Mawile are all easily 2HKOed by Earthquake, and Substitute protects Whiscash from the former two's Grass-type attacks. The last slot is dedicated to how you want Whiscash to handle the opponent's bulky Water- or Grass-type. Toxic is the best all around choice for weakening Dewgong, Wailord, and Bellossom in the long run but is easily worked around if the opponent has a cleric or is RestTalk. Hidden Power Grass deals some decent chip damage to Wailord and especially other Whiscash and Relicanth. Ice Beam will absolutely shred Tangela and deals a decent chunk to offensive Bellossom, and Earthquake + Ice Beam has pretty stellar coverage in the tier.
[ADDITIONAL SET COMMENTS]
It's not recommended to deviate from the EV spread given as it is specifically tailored to achieve the KOes Whiscash needs. However, a different nature can be used depending on how you would like Whiscash to fair against other threats outside of defensive stall teams. This Whiscash set thrives on Spikes support to weaken the opponent's bulky Water-type and help Whiscash nab the KOes that it wants to. Roselia is the best option as it covers Whiscash's Grass-type weakness perfectly, although Glalie can be used as a teammate since this set fits well on the offensive teams that Glalie works best on. Pokemon that can lure in and eliminate the opponent's Water-type will also work wonders here, with a screen lure such as Piloswine and Metang or specially offensive Flareon making particularly good choices. Finally, Pokemon that work best with the opponent's stall core broken up are needed to make the most of this set. Late-game sweepers such as Huntail, Pidgeot, and Bellossom would be among the best choices.
A fully specially defensive set is doable but ultimately strictly outclassed by Dewgong and Wailord due to Whiscash's unfortunate weakness to Grass-type attacks, which ultimately makes it an ineffective check to Fire- and Water-types that typically carry Hidden Power Grass. Rock Tomb and Icy Wind are interesting options considering Whiscash's middling Speed stat, potentially allowing it to tank an attack from, say, Haunter and finishing it off the following turn with Surf. Spark is a cool option that allows Whiscash to run Grass, Electric, and Ice coverage all in one moveset, something very few other Pokemon can accomplish in NU, but Whiscash's Special Attack is pretty lackluster to make the most of it.
[Checks and Counters]
Bellossom is probably the best overall switch-in to Whiscash as it resists Whiscash's STAB attacks, doesn't take too much from Ice Beam, and can easily OHKO Whiscash with its Grass-type STAB moves. Roselia and Tangela will also both easily KO Whiscash but need to be more careful around Earthquake and Ice Beam, respectively. Pelipper and other bulky Water-types will usually take a pittance from Whiscash's moves and can threaten back with Hidden Power Grass more than it can threaten them, but all will dislike getting hit by Toxic. Especially strong physical attackers will still break even maximum Defense Whiscash, such as Choice Band Flareon and Kingler. Finally, most anything else with a Grass-type attack, such as Haunter, Plusle, Venomoth, and Huntail, can consider themselves an effective check to Whiscash.