The fairies influence A Midsummer Night's Dream by creating both the conflict and the resolution. The term conflict is used to describe the oppositions or problems the characters face in the story line. A conflict can be between two characters, a group of characters, or even circumstances such as fate, nature, or society (Dr. Wheeler, "Literary Terms and Definitions: C"). The resolution is the moment when all of the conflicts are solved and the final outcome of the story is revealed.
The fairies, especially Puck, are responsible for creating the play's conflicts through the use of the magical flower. When Oberon sees Demetrius treat Helena, who is in love with him, horribly, Oberon instructs Puck to use the magical love flower, not just on Oberon's wife for revenge, but also on Demetrius. Oberon's goal was to fix Helena's love problems. However, Oberon only said that Puck would "know the man / By the Athenian garments he hath on" (II.i.268-29). Neither Oberon nor Puck were aware that there were actually two pairs of Athenian lovers in the forest that night. As a result, Puck enchants Lysander with the flower to fall in love with Helena instead, then mixes things up even further when he next makes even Demetrius fall in love with Helena as well. This mix-up creates emotional conflicts between the two men who challenge each other for Helena, between the two women who now distrust each other, and even between Hermia and both Lysander and Demetrius because they now hate her. The conflict even breaks up Hermia and Helena's friendship, who have been inseparable since childhood.
However, Puck, upon Oberon's command, is also responsible for creating the play's resolution by using magic to pair the couple's correctly. Puck's act of correctly pairing the couples even puts an end to the conflict between Hermia and her father because once Demetrius explains to Duke Theseus that he is now back in love with Helena, whom he was engaged to before he started pursuing Hermia, Theseus decides to override Egeus's request for the full force of the law should Hermia continue to refuse to marry Demetrius. Theseus decides to let Demetrius marry Helena and Lysander marry Hermia as we see in his lines:
Egeus, I will overbear your will;
For in the temple, by and by, with us
These couples shall eternally be knit. (IV.i.180-82)