The phrase "perfect foil" refers to someone or something that contrasts or complements another person or thing in a way that highlights their qualities or characteristics. Full definition
As his more discerning comrades, John Hawkes and Stephen Spinella prove perfect foils for Spader's particular theatricality. (smellslikescreenspirit.com)
Akuma has succumbed to a power that makes him an absolute perfect foil for the Mishimas. (cinemablend.com)
A solid midfielder who has the skill to be a contributor in the passing game, Matuidi would be perfect foil for Miralem Pjanic to bomb forward at will while keeping the area in front of the defence clear. (blackwhitereadallover.com)