Raichu, the Luigi of Pokémon. Seriously, Pikachu is the mega-Star getting all of Gamefreak's and the general population's love, while Raichu has to settle itself with Pikachu's scraps. That being said, Pikachu's scraps are something that other Pokémon would kill for. Raichu has a shockingly wide movepool, both with reliable Grass and Water coverage, which is a rarity on Electric types post Hidden Power's removal and a wide variety of support moves that give it niche's in a wide variety of formats. Base 110 Speed is nothing too shabby either and works well with Raichu's support sets.
Sadly that is where the good news ends. Raichu is as frail as you would expect a mouse to be, and its Offense is subpar without boosting with Nasty Plot, for which Raichu lacks the bulk and resistances to find a chance to do so. Additionally, Raichu is wholly outclassed by Raikou who has similar coverage, superior bulk and attack, Whimsicott outclasses it in support capabilities thanks to Prankster and superior typing, and Regieleki who has far superior Speed and Electrical power. However, Raichu's unique blend of traits ensures that it maintains a niche all to its own.
Lightning Tag Team
Raichu
Ability: Lightning Rod
Item: Focus Sash
-Fake Out
-Encore
-Nuzzle
-Volt Switch
Nature: Timid (+SPE, -ATK)
EVs: 252 HP / 4 DEF / 252 SPE
Raichu still makes an excellent doubles pick thanks to its neat support capabilities. Fake Out is a fantastic disruption tool, and thanks to Raichu's high speed over other common fake out users like Rillaboom and Incineroar, has a good chance of going off. This also pairs well with Encore -opponent used Fake Out last turn? Trap them in with Encore. Also works with other setup moves like Flying types with Tailwind, Screens from a variety of Pokémon, Protect, etc. Encore is brutal and timed correctly can shutdown an opponent for several turns or force them to switch out of what could otherwise be a favorable match up. Nuzzle is a unique boon to the Pikaclones, being a reliable Thunder Wave that isn't blocked by Taunt and provides excellent speed control as a result. Volt Switch rounds out the set, acting as a "slow" pivot, able to punish predicted switches or just to get Raichu the heck out of dodge while ensuring it has some damaging capability if it is the last Pokémon standing.
Lightning Rod is how Raichu stands out from its competitors. Electric weak picks like Kyogre, Tornadus, Yveltal, and Charizard can all stop worrying about Regieleki with Raichu on the scene, as the protection provided is invaluable in keeping your heavy hitters up. Also combos well with Encore -lock your opponent into an Electric attack and watch them squirm.
Other Options
Feint -Protect is the best move in VGC, and this breaks it. Also nice priority for picking off targets who are hanging on by a Focus Sash.
Endeavor -excellent support option, especially given Raichu's poor HP, but Event locked, so if you don't have the event Pokémon, not an option (may also not be legal for current formats -not sure).