I tried the ladder challenge but got hung up in the 1600's with a ludicolo and a kabutops, so I'm not sure how I'll do on this next one. However, I do plan to try under the alt. speedghilliesniper since it's been reset since when I originally used it. In the mean time , here's a set that I'v been using that I'd like some opinions on.
Magneton @ Eviolite
HP:50 ATK:60 DEF:95 SPA:120
Trait: Magnet Pull
EV's: 252HP / 164Def / 92spa
Nature: Modest (+spa, -atk)
Some of the biggest pains to rain teams are opposing steel types, especially those who's only weakness is fire. This set aims to trap and eliminate the 2 most notable, Ferroseed and Escavalier. Against Ferroseed magic coat is used to stall rain on Ferroseed to keep a spiteful player from setting up hazards or leech seed until rain runs out, forcing it to attack with it's pitifully weak gyro ball or seed bomb that does less than 10%. Escavalier is much more straight forward, with it being able to 3HKO at best with megahorn while Magneton can 2HKO with thunder under rain , 2HKO with HP fire outside of rain, or any combination of the 2. Another notable threat it stops that plagues rain teams is cosmic power Sigilyph. While Magneton can't trap it, stored power wont 2HKO without a ludicrous amount of boosts, while thunder will 2HKO through 2 rounds of cosmic power meaning you can come in on a cosmic power or psycho shift and 2HKO the totem pole under rain with 100% accurate thunders. Metal boost brings previously untouchable Sigilyphs boosted very high back to 2HKO range, while also softening special walls previously tough to break through such as Slowking. It also checks other water types reasonably well, walls most grass types effortlessly, and in general acts as a very good bulky pivot. Another interesting function is that with magic coat it works as an interesting Smeargle anti lead, bouncing spore back, although one must be wary of it waking back up and sporing you again so if you can predict when it will wake up you can always beat it by using magic coat.
Being a more specialized and situational set, this has trouble with quite a few things. It's main hurdle is ground types, and to a lesser extent fighting types. Ground types or even pokes who run ground moves are often able to OHKO, while fighting types can either KO it out right or set up on it. It also struggles against electric types such as Lanturn, Manectric, and Electrivire.
With these threats in mind, bulky levitating psychic types would seem to fit the bill as counters to these threats, and either the newly dropped Cresselia or Uxie both do exactly this while also adding some valuable support with their bulk and versatile move pools to benefit your team however you need. Both of these pokes also greatly appreciate Escavalier gone as it allows them to function much more effectively.
Substitute and charge beam can be used to set up on trapped Ferroseed, although this generally isn't recommended as you'll more than likely end up with a full set of hazards on your side of the field. Magnet rise can be used over magic coat to eliminate it's ground weakness if you wish to trap opposing Steelix and help remedy it's ground weakness in general, however on a rain team Steelix is less of a pain than usual, it still can't touch ground types such as Sandslash that it now walls and Ferroseed will again set up multiple layers of hazards. Damp rock can be used to extend the precious rain these teams run on, but the lack of bulk is undesirable as it will leave it vulnerable to being 2HKO by cb Escavalier. Volt switch can be used if you prefer the momentum gained after kill by giving a slow switch into a better setter or sweeper. Hidden power ground can be used over hidden power fire if you wish to hit electric types rather than quickly dispatch of Ferroseed, although with this it can no longer reliably stop Escavalier outside of the rain.
Just for Pocket, here's a replay showcasing what it does to Ferroseed.
It's worth noting since this I'v switched Amoonguss and Stoutland for Cresselia and Escavalier respectively.