The phrase "ideal foil" refers to a person who contrasts or complements another person's qualities, highlighting their strengths or weaknesses. Full definition
i have lots of chard left in the garden & this soup looks like the ideal foil to the cool Canadian autumn weather. (101cookbooks.com)
Charring them on the cut side concentrates their flavor and somehow makes them even more succulent, an ideal foil for lush crème fraîche and avocado. (bonappetit.com)
From what I have seen with Lacazette he is good in tight spaces, has a decent first touch and the passing / creative part of his game is not too bad so could be the ideal foil for someone like Auba. (justarsenal.com)