Dumb idea: Malphite is a mountain, right?
Like, he's a literal walking mountain who probably shatters regular villages by accident from the mere shockwaves of his footsteps alone. Possibly unaware of the living creatures under his feet.
So what if his auto attacks naturally have an AoE effect to them? Like make it so his passive is just AoE auto attacks. Would probably help paint him as this colossal being when even his lightest touch sends shockwaves across the field.