Offensive Rain is a lesser used Strategy in Little Cup, mostly because it lacks a Drizzle user. Even without a permanent weather starter, Rain can be a very effective strategy if used correctly. Rain Dance teams revolve around Swift Swim abusers with powerful double STAB Water-type attacks, however because of the general lack of overpowering rain abusers, it not a commonly used strategy.
There are few good pokemon to set up rain. While one might think that rain teams require a Damp Rock to start weather, Eviolite is generally the better item. Bulky Water-types, such as Staryu and Chinchou, are great users of Rain Dance, being able to fire off rain-boosted STAB Hydro pumps and perfect accuracy Thunders in the Rain. Bronzor and Mienfoo are other great examples of Rain Dance users, the former having great typing and the ability to use Stealth Rock, while the latter being able to check many threats to a rain team, such as Lileep and Ferroseed.
There are only a few viable Swift Swim abusers, many of whom can set up Rain on their own, but most are special based because of the difference in base power between the physical Water STAB, Waterfall, and the special variant, Hydro Pump. Because of this a good rain team, needs a good amount of physical attackers, preferably Fighting-types to combat Lileep and Ferroseed, two of the best Rain counters.