Oberon's magic potion is ironic because although the potion is a potion of love, he uses the potion to get revenge on his wife and to get his own way with the changeling boy. Because he uses the potion in a selfish way, one can question whether he truly loves Titania or not.
He also uses the potion to help "fix" the situation between Helena and Demetrius. His meddling in their affairs, however, results in chaos not love, and although the characters seem to all be happy in the end, the reader knows that Demetrius only loves Helena because of the potion in his eyes. The reader is left questioning whether his love is real and whether or not a love that is forced is even love at all.