Geomancy Infernape Sweep
Assist randomly selects an ally's move, in this case Smeargle's Geomancy (doubles Special Attack, Special Defense, and Speed), which can be be used in one turn because of Infernape's Power Herb. Smeargle also has extra utility with Counter, Mirror Coat, and Destiny Bond, which can't be selected by Assist.
Infernape @ Power Herb
Ability: Blaze
EVs: 252 HP / 4 Def / 252 SpA
Modest Nature
Assist
Flamethrower
Focus Blast
Grass Knot
Smeargle @ Focus Sash
Ability: Own Tempo
EVs: 252 HP / 4 Def / 252 Spe
Timid Nature
IVs: 0 Atk
Geomancy
Counter
Mirror Coat
Destiny Bond
Special thanks to Mario Castañuelas and oodogla 1313 for the idea.
Music: Prelude to the Holberg Suite by Edvard Grieg.
Serenade in G major (K.525) by Mozart