Blastoise, the Cannon Turtle pokémon (why Shellfish?) the series first water starter, Blastoise has had a rough history. Lacking the burning popularity of Charizard and the reliable consistency of Venusaur, Blastoise has been made to languish in shadows throughout the generations. Blastoise has received a lot of love over the years -getting a Mega Evolution increased its movepool considerably on top of being a generation I pokémon, but Blastoise has the same condition as Meganium. Its stats are too balanced and average, which gives it a lot of variety but without a defined role, Blastoise is constantly outclassed by the competition.
Maxim 34
Blastoise
Ability: Torrent
Item: Choice Specs
-Hydro Pump/Scald
-Focus Blast/Aura Sphere
-Ice Beam
-Dark Pulse/Scald
Nature: Modest (+SATK, -ATK)
EVs: 252 HP/4 DEF/252 SATK OR 4 HP/252 SATK/252 SPE
"If you're leaving scorch marks, you need a bigger gun." Blastoise has quite the wide movepool to make it an effective Special Sweeper, using its above average bulk to muscle through attacks, while its speed puts it ahead of most dedicated tanks. Hydro Pump is STAB of choice hitting many targets hard, Ice Beam hits most popular Water resists (Dragon and Grass), Focus Blast has great coverage, and Dark Pulse covers a few targets missed by the other moves. Alternatively, Scald is a choice for a more reliable water STAB that provides support by threatening burns on switch-ins.
Blastoise's lack of pure power shows: most targets that aren't weak (or are weak but just THAT bulky like Umbreon) to its moves are only 2HKOs with Hydro Pump or Focus Blast at best. However, Blastoise's natural bulk comes to its advantage here: it can often take a hit or 2, giving it plenty of time to land that 2nd or 3rd hit ncessary for the KO, though the unreliability of Hydro Pump and Focus Blast do hurt. The bulk also enables Blastoise to reliably get to Torrent range, making its Hydro Pumps a force of nature to be respected.
Two Cannons, Hold the Turtle
Blastoise
Ability: Torrent/Rain Dish
Item: Life Orb/White Herb
-Shell Smash
-Hydro Pump/Aqua Tail
-Dark Pulse/Ice Beam
-Earthquake/Focus Blast
Nature: Mild (+SATK, -DEF) OR Lonely (+ATK, -DEF)
EVs: 4 ATK/252 SATK/252 SPE OR 252 ATK/4 SATK/252 SPE
To be honest I was surprised that Blastoise got Shell Smash. I shouldn't be, but I was. And Blastoise makes quite the terrifying Shell Smash sweeper, able to abuse its wide movepool and balanced stats to full effect. After a single Shell Smash, Blastoise surges past most of the unboosted game (and some of the boosted too), including Dragapult, Zacian, positive speed Nature Scarfed targets below base speed of 108 with a neutral speed nature. Many bulky targets are cleanly 2HKOd by move of choice (often the Water STAB) while frailer targets are blown away. Item choice is up to preference. Life Orb has amazing power, but makes Blastoise so incredibly frail after a Smash, while a White Herb allows Blastoise to maintain its above average defenses while running roughshod over the opponent's team.
Water Types Outclass Blastoise
Specs:
Primarena -Boasts far more powerful Specs attacks alongside a secondary STAB, a better defensive typing and better Special Bulk.
Inteleon -Much faster and again possesses far stronger attacks than Blastoise, though Inteleon's poor movepool really hurts and can't take a hit for beans.
Shell Smash:
Cloyster -Possesses greater ATK and far more powerful moves in Skill Link Icicle Spear and Rock Blast, and great physical DEF, even after a Shell Smash, though Blastoise is naturally faster and can take special hits before a Shell Smash. Both have the same SATK.