These two seem like they'd work fairly well as a tag team, with the right support from the rest of the team.
Araquanid @ Waterium Z
Water Bubble
Adamant
248 HP, 252 Atk, 8 SpDef
- Liquidation
- Lunge
- Rain Dance
- Crunch/Poison Jab/Surf/Scald/Power Split
One of the big new powerhouses, this thing deals some incredible damage with Liquidation, thanks to Water Bubble converting it to 170 base power before STAB. This set is made to ensure it has the deadliest possible attack; STAB multiplies the damage by 1.5 times, and rain multiplies it by ANOTHER 1.5 times, meaning we're looking at a 382 BP Liquidation, and a 720 BP Hydro Vortex. Lunge is secondary STAB to use against Water-resistant enemies (in particular things with dual-Water resist, like Kingdra) as well as the Atk drop, and Rain Dance is just to put up rain if you get the chance. Crunch and Poison Jab both provide additional coverage, but in all honesty I'm not sure how useful it is, and sadly enough Araquanid doesn't get access to any Grass moves to help it counter things like Vaporeon and Gastrodon. Surf and Scald are options if you want Special coverage, with them having 180 and 160 BP respectively (405 and 360 respectively with STAB and rain factored in, and 787 or 720 BP Hydro Vortex). Power Split is also useful if you're facing enemies with particularly high Atk, and if you're willing to drop the HP EVs for Speed and use Normalium Z, you can get a Speed boost on top of that. You could also use Life Orb, giving up Hydro Vortex for additional power on your non-Water moves, but in that case I'd probably swap Lunge for Leech Life to give it some recovery.
Pelipper @ Damp Rock
Drizzle
Bold
248 HP, 252 Def, 8 SpAtt
- Hurricane
- Scald
- U-Turn
- Roost
Where Araquanid has great natural special bulk, Pelipper is great on the physical side of things, and has a new toy to play with in the form of Drizzle, making it an interesting alternative to Politoed. Hurricane takes advantage of the rain by being boosted to 100% accuracy, while Scald has its BP boosted to 120 before STAB. U-Turn is there purely to switch Pelipper out into something else, and Roost keeps it from dying due to switching in on Rocks. Not too much needs to be said here.
So what are the downsides of this pairing? Well, they share two common weaknesses: Electric and Rock. This means you will have issues dealing with fast, powerful Rock types like Lycanroc and Nihilego if the wrong one of the pair is in, and a strong enough Thunderbolt, Thunder, or Hurricane will rock their worlds. Speaking of Rock, Stealth Rocks can be a problem as well, as both will lose 25% health to them, and while each has decent enough bulk, that is a pretty heavy blow. Third, and probably most important, is the plethora of Water Absorb, Storm Drain, and Dry Skin pokemon that could just eat up Araquanid's Liquidations. Vaporeon and Gastrodon are probably the two biggest threats in this case, but there's also the threat of things like Mantine, Maractus, Seismitoad, defensive Araquanid, Cradily, Heliolisk, and Jynx, among several others. Your best bet is to have a powerful Grass type user on your side. Kartana in fact is probably an ideal teammate. You'll also want something that can easily spin away rocks, putting Tsareena and Dhelmise up there as potential partners. Jolteon may be a decent team member as well to take advantage of the rain via Thunder.
