The Pikachu of Mercy (Double Battle Supporter Gen 7)
Item: Focus Sash (No one shotting this time.)
Nature: Relaxed (Sacrifices Spd for Def making it live a bit longer.)
EV's 252 Spd 126 Def 126 Sp. Def
Surf: Handles Ground Typings plus helps allies with abilities like Water Absorb, Storm Drain, and Dry Skin.
Discharge: STAB plus damage other Pokemon plus helps allies with abilities like Lighting Rod, Motor Drive, and Volt Absorb.
Volt Tackle: STAB plus paralysis. Needed for Catastropika (Ya gotta defend yourself in some way)
Grass Knot: In case of heavy Ground typings or Water/Ground plus helps allies with abilities like Sap Sipper. (If you aim at the ally that is!)
This can be used in a way like how most people use Smeargle, A stat boosting or HP helper. Just this time using attacking moves. Think of it like the attacking-but-helping Smeargle.
To get a Pikachu with Surf, transfer the Pikachu in Pokemon Yellow or if playing in USUM, become champion in all the surfing spots.