Carvanha is a really dangerous Pokémon. It has access to Speed Boost, allowing it to outspeed every unboosted Pokémon after protect, and its base 90 Attack puts the hurt on its opponents. It generally runs Hydro Pump / Crunch / Ice Beam / Protect, allowing it to get past physically bulky Pokémon and Tangela.
Remove mention of Tangela, change Ice Beam to Destiny Bond.
Corphish got a huge buff in XY, getting Aqua Jet, and to a lesser extent Switcheroo, added to its moveset. With Aqua Jet and Life Orb, Corphish is able to threaten nearly every offensive Pokemon in the metagame. Hitting Gligar with SUper Effective priority is pretty great too. Corphish's Crabhammer is so strong, that most Water-type resists other than Tangela won't be able to tank them at all. Beyond this, Corphish has an excellent movepool in Swords Dance, Dragon Dance, Superpower, Ice Beam and more, making it an excellent wallbreaker in XY.
Also, should mention something about Adaptability. And Waterfall is better.
Tirtouga is arguably the best Shell Smash user in the tier, due to its access to Sturdy and Berry Juice, along with high-powered STABs to basically have two hits against any pokémon after setting up. It generally uses a mixed set using Ice Beam to break through Gligar and Tangela.
Now they use Aqua Jet or Earthquake instead of Ice Beam.
Shellos is one of the better defensive Water-types. Access to Recover, really good defense stats, Sticky Hold, along with Clear Smog and Scald makes Shellos unique. It is the most reliable Sneasel counter around, while it can fairly easily check Swirlix. It has a decent Special Attack Stat, and the 30% Burn rate of Scald can ruin an opposing Physical Attacker. It is still an excellent Special tank, as even Tangela cannot hope to inflict more than 55% to it with Giga Drain.
Vullaby uses a combination of bulk, Overcoat, and a good bunch of resistances to act as a strong choice for defensive teams. Furthermore, its Flying typing is a godsend in dealing with Scraggy and Tangela, two Pokémon who tend to give many teams trouble. Furthermore, it can reliably switch into Misdreavus, which isn't a common feat.Vullaby has access to Knock Off and Defog, which make Vullaby able to support her teammates very well.
Change Tangela to "Chlorophyll sweepers and Foongus".