How is Macduff a foil to Macbeth? Which scene can prove i?

While he is supposed to be attending a banquet, Macduff sneaks away to England to consort with Malcom and raise an army to attack Macbeth.

He is the mysterious person "not of woman born" (he was saved as a baby by a Caeserian section) who approaches Macbeth's castle with his soldiers hidden behind tree branches. (In such a way the forest "moves" as foretold in the prophecy.)

Macduff uses stealth, cunning and ruse to overpower Macbeth.

Check out the reference below to locate the exact lines you are looking for. If you are after the final confrontation scene justs before he kills Macbeth, it is Act V.Scene viii.lines 15-16.