He has the ability to change shape and can also change his voice. We know this because he led Lysander and Demetrius into the woods by imitating the voices of other people calling them. The next day made it all seem like a dream. At first, he had to separate the four Athenians and then bring them back to an area where they will all be at the same time, but will not be aware of each other's presence. He then gives Lysander the antidote, along with Titania, also in the same sleeping area with Bottom. Again, if it were up to Puck, Titania would have been stuck with Bottom. Oberon was satisfied because Titania had given up shapeshifting and thought she was suffering