Lightning

Check who you are fighting before you commit to Lightning. Rubber users are immune to both its damage and its stuns, and no other fruit gets shut down that completely.

Against everyone else, the reworked Rumble is one of the most versatile Legendaries around. You become lightning, dash across the battlefield so fast it looks like teleporting and call thunderstorms that paralyze enemies. For grinding, Elemental Reflex plus large AoE keeps it viable in all three seas, and [X] Thunderstorm followed by [Z] Lightning Orb stuns mobs and disables their moves while you hit them with your Fighting Style. In PvP it works as stun support for Swords and Guns, most moves break Instinct, and it does very well against Magnet users.

We would not pick it for air fights: [X] and [V] rarely land when you are off the ground. Damage comes in separate parts, so totals are low and inconsistent, and saving the charges on your back for [F] gets tedious. Those glowing charges also drop FPS on weaker devices.