Stunfisk Galar should be ranked right below whatever Bronzong is because of this set.
[SET]
name: Specially Defensive
move 1: Earthquake
move 2: Stealth Rock
move 3: Yawn
move 4: Protect
item: Leftovers
nature: Careful
ability: Mimicry
evs: 252 HP / 4 Atk / 252 SpD
[SET COMMENTS]
Galar Stunfisk serves as a defensive niche in two ways: it counters extremely powerful special wallbreakers like Toxtricity and it can also reliably set up Stealth Rock. While Galar Stunfisk's role in the tier is often overshadowed by Bronzong and even Steelix, Stunfisk's greater special bulk compared to both of these Pokemon and Electric immunity compared to Bronzong make it a good choice for teams struggling with Toxtricity. Meanwhile, Galar Stunfisk is still a good defensive check to many of the Pokemon Bronzong normally counters like Roserade. Earthquake is Stunfisk's STAB of choice and has good coverage by itself in UU, hitting many threats that could otherwise switch into Stunfisk like Incineroar and Lucario for respectable damage while also damaging the threats Stunfisk is supposed to counter like Gardevoir and Choice Specs Sylveon. Yawn and Protect form a combination that can force out threats while also keeping Stunfisk's Stealth Rock against prominent Defoggers like Noivern and Rotom-Wash. Unfortunately, Stunfisk has very limited move options so there is essentially no deviation from this set - the common defensive idea of Toxic stalling is not available since Galar Stunfisk does not learn Toxic nor does Galar Stunfisk has access to a decent steel STAB move to more badly damage Fairies and Noivern. Absolute maximum special bulk allows Stunfisk to more easily switch into Choice Specs Sylveon and Toxtricity, while also letting Stunfisk still strongly check Roserade as the initial Leaf Storm from Leftovers offensive Roserade does 47% maximum. Mimicry is Stunfisk's only ability and rarely changes gameplay except against Indeedee's Psychic terrain, which changes Stunfisk Galar to a pure Pyschic type for as long as the terrain is active.
Galar Stunfisk fits best on more defensive balanced teams that need a strong response to Toxtricity. Generally, it fits on teams where Bronzong would be appreciated but the need to counter strong Electric attackers like Heliolisk and Toxtricity is more important than Bronzong's Levitate which lets it be a strong check to threats like Rhyperior and Flygon. Since Galar Stunfisk has no recovery options outside Leftovers + Protect and an unreliable Pain Split, Wish support from Sylveon and Umbreon, which also provide cleric support, is helpful to keep Galar Stunfisk healthy throughout a game. Sylveon in particular can absorb many Fighting moves that trouble Stunfisk like Choice Band Pangoro's Close Combat - especially notable because Stunfisk can use Protect to scout the tier's many Choice item Pokemon. is often Passive Pokemon like Vaporeon, Sylveon, and Bronzong that sun teams take advantage of appreciate Arcanine's ability to hard-check Venusaur. Because Stunfisk is weak to Water and Fire and can check the most prominent Grass type in the tier, Roserade, bulky water partners like Milotic are appreciated to be able to switch into threats like Darmanitan and Intelon. Again, Galar Stunfisk's Protect frequently comes into play against these offensive threats because they often run Choice items, and Stunfisk can easily absorb U-Turns from these Pokemon should they over predict against a bulky water switch in.
In terms of play, while Galar Stunfisk is generally a normal defensive Pokemon, the Yawn and Protect combination mentioned before is a rare tactic that can be explained further. As Defoggers like Noivern or Rotom-W switch in, Stunfisk will often be using Stealth Rock. The Stunfisk user has to predict the Defog and Yawn on that turn - the next turn they can Protect on an attack or Stealth Rock on a predicted switch. Since the Defogger will now be asleep, the hazards stay on and the Galar Stunfisk user can switch into a Pokemon to force the Defogger out - for this reason, Roserade is a good partner to force out Rotom-W. Roserade also can provide Spikes which makes Yawn a more powerful phazing move.