Pikachu is a glass-cannon physical or special attacker in VGC, relying entirely on the Light Ball item to double its offensive stats. While extremely fragile, its high damage output and priority moves like Fake Out allow it to pressure opponents before it gets hit.
Pikachu pairs best with redirection support from Clefairy to protect its frail defenses, and speed control allies like Whimsicott with Tailwind to ensure it moves first.
Defeating Pikachu involves exploiting its fragile bulk.
Incineroar is a major counter, reducing its physical threat with Intimidate and matching its Fake Out pressure while threatening a KO with Flare Blitz.
Kingambit also counters it, easily absorbing its attacks with its high bulk and threatening a KO with priority Sucker Punch.
The best moveset for Pikachu in the current competitive meta typically features the moves Fake Out, Thunder, Alluring Voice, Volt Tackle.
In the Pokémon Champions meta, Pikachu can be countered by exploiting its weaknesses (ground 2x) and using effective check/counter teams.
The best item for Pikachu is typically Light Ball, based on high-level tournament and ladder stats.