Sharpedo, the mascot of Team Aqua, whose claim to fame is its overwhelming fragility. I mean seriously, 70/40/40 Defenses is outright pitiful. And its speed is lackluster despite being so frail at only a base 95. However the successive generations have given Sharpedo a good number of tools. Speed Boost in Gen V, a potent Mega Evolution in Gen VI... which Sword and Shield promptly took away. Sharpedo lives fast and dies fast, and while it may not offer any defensive utility, make no mistake, Sharpedo will chew through an opposing team given the chance.
E and F
Sharpedo
Ability: Speed Boost
Item: Life Orb
-Protect
-Liquidation/Hydro Pump
-Crunch
-Close Combat/Psychic Fangs
Nature: Lonely (+ATK, -DEF), Naughty (+ATK, -SDEF) OR Adamant (+ATK, -SATK)
EVs: 252 ATK/4 SATK/252 SPE
Sharpedo thrives on offense, coming in, Protecting and going for the kill. Protect is necessary, as Sharpedo's base 95 is easily outsped and Sharpedo cannot survive a turn without the Protection. One Speed Boost later and Sharpedo outspeeds the entire tier. After that, moves are fairly standard. Crunch and Liquidation for STAB with Close Combat and Psychic Fangs for coverage. Close Combat takes care of opposing Dark and certain Steel types like Cobalion, Crawdaunt, Hydreigon, and Zarude, while Psychic Fangs hits Keldeo, Dragalge, Heracross, Roserade, Virizion and Toxicroak hard.
Hydro Pump is an alternative option for a Water STAB, as many Water weak targets have higher DEF than SDEF to the point that an uninvensted Hydro Pump is still the stronger option.
Shark Cannon
Sharpedo
Ability: Speed Boost
Item: Life Orb
-Protect
-Hydro Pump
-Dark Pulse
-Ice Beam/Close Combat/Psychic Fangs
Nature: Rash (+SATK, -SDEF), Mild (+SATK, -DEF) OR Modest (+SATK, -ATK)
EVs: 4 HP/252 SATK/252 SPE
Second verse, flipped from the first. Special Variant of Sharpedo, which still hits plenty hard on the special side. For coverage moves, Ice Beam is worth a consideration due to its ability to threaten Grass and Dragon types.
Other Options
-Flip Turn -STAB U-Turn on Sharpedo? Yes please. However, with Protect, Sharpedo is already starved for move slots as it is and Flip Turn is far too weak to be the main Water STAB
-Aqua Jet -Priority is good for countering Priority
-Substitute -An alternative over Protect. Come in on a naturally slower opponent who may use Sharpedo to setup expecting the Protect and throw up a Sub, giving Sharpedo protection while it proceeds to blast through the opposing team. However, this A) leaves Sharpedo exposed to naturally faster threats without Protect, B) Puts Sharpedo on an even shorter timer between Life Orb and entry hazards and C) not worth running both Protect and Substitute on the same set. Loss of coverage is too great.
-Taunt -Similar to Substitute, prevents opponents from capitalizing on Sharpedo's expected Protect and enables Sharpedo to mess with walls who think they can safely tank it.
-Poison Jab -Hits Primarina, the Tapus, Togekiss, and Virizion.
-Destiny Bond -Good for Sharpedo to remove a target you know can take it out, but Sharpedo can't take out itself.
Dynamax Corner
Sharpedo has several excellent options when Dynamaxing. Max Geyser sets up Rain, making Sharpedo's primary STAB a monster, while a Psychic Fangs powered Max Mindstorm provides excellent protection vs Priority. Max Knuckle (Close Combat) and Max Darkness (...any Dark STAB) compliment physical and special offense respectively. Speed Boost means Sharpedo can forgo the Max Windstream (Bounce).