Yay, one of my ferrets is up!
Overview
I really like Floatzel. Unfortunately, GameFreak wasn't quite as kind to it when they made it. Don't get me wrong: Floatzel has some key positives. Base 105 Attack and Base 115 Speed are really good, as they allow Floatzel to hit hard and fast. Base 85 HP and Sp. Attack aren't too bad, and the Sp. Attack allows for a bit of mixed sweeping potential. Sadly, the two big things that hinder Floatzel from being a top-tier threat (where I would like it to be) are its pitiful defenses (Base 55 and 50 suck) and a slightly less-than-stellar movepool, especially if you are restricted to Kalos-native Pokemon. Don't get me wrong, Floatzel is a great Pokemon and I love it a lot. Unfortunately, it has some issues that really keep it in check. Don't be afraid to try him, though!
Abilities:
Swift Swim: Under "Rain" weather, Floatzel's Speed is doubled. This ability is not quite as useful now due to Drizzle's nerf (not that Swift Swim + Drizzle was legal in OU down last gen...), plus, as someone else pointed out, it makes you a target for Thunder because of its perfect accuracy in said weather. Still, it really ensures that Floatzel will move first almost all the time.
Water Veil: Floatzel cannot be affected by the "Burned" status condition. I'm a bit partial to this one, myself, just because it is not weather dependent. Still, it is also situational, but at least Floatzel won't have to worry about the Attack drop from Burn.
Sets:
I'll start with something a little different.
Why is that weasel carrying a baton?
-Bulk Up/Agility
-Waterfall
-Substitute/Aqua Ring/Return
-Baton Pass
Item: Leftovers/Life Orb
Ability: Water Veil/Swift Swim
Nature: Jolly (+Speed, -Sp. Attack)/Adamant (+Attack, -Sp. Attack)
EVs: 252 HP, 4 Sp. Defense, 252 Speed -or- 252 Attack, 4 Sp. Defense, 252 Speed
Let me first say that this set isn't likely to sweep on its own. I would love to see a variation that does, though (or make one myself, ha ha). But since Floatzel can use Baton Pass and is fast, it is likely to be able to get a boost or two before passing a boost to an ally. Bulk Up boost Attack and Defense, Agility boosts Speed. Waterfall is solid damage that gets same-type-attack-bonus (STAB) and has a nifty flinch chance that works well with Floatzel's high Speed. Substitute and Aqua Ring give a more defensive flavor to what Floatzel can give, and Baton Pass is obvious. Return is listed if you'd like Floatzel to be more of a sweeper after receiving several boosts instead of providing them for the team.
The item, ability, nature, and EVs are dependent on whether or not Floatzel is intended to support or sweep. Support Floatzel should run Leftovers for HP recovery, Water Veil to prevent wear down of Burn, a Jolly nature to ensure high speed, and the max HP and Speed to ensure Floatzel can pass on boosts. A sweeper should have the others listed to max out damage potential, and Return should definitely be run in such a case.
Weasel Beatdown
-Waterfall/Aqua Tail
-Ice Punch/Ice Beam
-Focus Blast
-Aqua Jet/Rain Dance
Item: Life Orb
Ability: Swift Swim/Water Veil
Nature: Naughty (+Attack, -Sp. Defense)
EVs: 252 Attack, 4 Defense, 252 Sp. Attack
I'm also going to disclaim here that this set accounts for being in the rain, which is why no Speed EVs are run. Anyways, this set attempts to, with the proper support, break stuff up nice. Waterfall versus Aqua Tail comes down to reliability and a flinch chance versus more power and slightly less accuracy. Ice Punch is great, but if non Kalos-native Pokemon are banned, Ice Beam is your only choice. Focus Miss is great coverage and power when it hits. Aqua Jet is to prevent other priority users (minus the rare Extremespeed) from getting the jump on Floatzel. Rain Dance helps keep rain up if Floatzel doesn't need to have priority, but it has no bulk to stomach a hit, so Aqua Jet is generally preferred.
Like I said, the EVs are assuming you have rain support, since Floatzel has 532 Speed in the rain without any investment and is likely to move first. Outside of that, though, the EVs should be adjusted. The nature allows Floatzel to go mixed, and the Life Orb boosts Floatzel's power.
And just to appease me a bit...something less creative.
A Weasel with a Headband
-Waterfall/Aqua Tail
-Return
-Ice Punch/Ice Fang
-Aqua Jet
Item: Choice Band
Ability: Swift Swim/Water Veil
Nature: Adamant (+Attack, -Sp. Attack)
EVs: 252 Attack, 4 Sp. Defense, 252 Speed
This set just aims to sweep without setting up and then switch out as necessary. Waterfall and Aqua Tail are the STABs again, choosing between reliability and power. Return is great coverage, which Ice Punch (Ice Fang if Kalos-native are only allowed) provides more coverage. Aqua Jet turns Floatzel into a priority revenge killer.
The Adamant nature and EVs maximize Attack and Speed, and a Jolly nature can be used if you don't have rain support and really need to outspeed more things. Beware that Floatzel will not hit as hard, though.
Other Options:
-Crunch provides coverage, but is generally not necessary.
-Brick Break is a physical Fighting-type move, but its base power is low, thus making it rather unappealing.
-Power-Up Punch (does damage and boosts the user's Attack by one stage) would be interesting on a set built around it, but I'm guessing that would be difficult to pull off.
Checks and Counters:
If it hits before Floatzel (somehow...), Floatzel is likely to fall. If it can stomach a hit and hit hard back, Floatzel is likely to fall. Sadly, Floatzel's main issue is that is is so frail, a glass cannon as some have called it. Paralysis and Sticky Web really kill Floatzel, as it can no longer hit before being hit outside of Aqua Jet. For the Baton Pass and Choice Band sets, entry hazards damage Floatzel every time it switches in, which is what those sets do.
Overall, Floatzel is still a great Pokemon that I love. It can really be beneficial to a team, although it requires some support to keep it from turning into a frail, dead-weight Pokemon.