The Sunshine weather effect is a field-altering effect that is available through the ability Drought and through the move Sunny Day, which can be learned by most pokemon. Bright sunlight has a number of useful effects that can completely alter the way a battle plays out- which makes it worth building a team, or a significant part of a team, around.
As with the other effects, Sunshine has a duration when created with Sunny Day of five turns, counting the turn it is created. This can be extended to ten turns if the pokemon that used Sunny Day is holding a Heat Rock, but that carries risks with it- the pokemon in question cannot hold another item instead, so you will want to make sure that it’s not something you’d rather have Leftovers or something else on. If it’s created by a pokemon with the Drought ability entering the battle, however, Sunshine will last until the weather is forcibly changed.
Sunshine has a number of interesting effects. First of all, it boosts Fire attacks by half and cuts Water attacks by half. Then there are the individual moves it effects-
Synthesis, Morning Sun, and Moonlight all max out in Sunshine and fully restore the user’s HP. Solarbeam stops needing a turn to charge, and Thunder and Hurricane suffer an accuracy drop from 70 to 50. Finally, Weather Ball becomes a Fire attack and its power doubles.
Some abilities are affected too. Chlorophyll, Leaf Guard, and Solar Power all become active in Sunshine. Dry Skin pokemon start taking 1/16 of their HP in damage every round and take double damage (on top of the weather boost) from Fire attacks. And Cherrim’s Flower Gift activates, boosting both its attack stats. Last of all, Castform becomes a Fire type pokemon.
With these effects, Sunshine gives you several opportunities and takes away others- so if you’re going to use it, make sure to prepare your team. With Water moves cut back, you may want to find another way to handle Fire, Rock, and Ground pokemon. At the same time, your pokemon of those types suddenly have less to worry about. Choosing Fire moves and Solarbeam to stick onto your team members helps you take advantage, and many Grass pokemon become a lot faster- but a lot frailer if your opponent is wielding Fire attacks. Dry Skin is a liability, so you likely won’t want Toxicroak on your team if you’re using Sunlight effects. Your opponent will likely become wary of putting out their Grass pokemon if the pokemon you’ve got active is capable of learning Fire attacks, and the same goes for any Bugs or Ice pokemon they have.
Some good pokemon to put with Sunny Day include Fire types like Infernape that are quick enough to take full advantage of Solarbeam without a charge turn, Grass types like Exeggutor that gain a huge boost in effectiveness from Synthesis, defensive pokemon with no Fire worries like Umbreon that can have Moonlight as a move, and Rock or Ground types like Steelix or Aerodactyl who have access to Fire moves (Fire Fang in this case) and benefit from effectively losing their weakness to Water.
Most notably, Camerupt loses part of its largest weakness and can pack both a Fire attack and Solarbeam, making it an excellent choice if you don’t mind its being otherwise mediocre- as a surprise-assault pokemon in Sunshine, it has some potential.
