Mercury enters one of the signs that it rules on the 21st May and goes OOB at 13° of the sign on the 27th remaining in this condition until the 17th of June when it will be at 20° Cancer.
Mercury is obviously in his element here, a rational and agile thinker open to new ideas and experimentations, puns and intellectual flexibility are also part of the game although Mercury is also the prankster of the zodiac and here words could be used to alter the truth in some way!
The OOB status could make this planet very versatile indeed with great curiosity and a real talent for the acquisition of knowledge.
On the 29th and 30th there will be transiting T-square in the mutable signs formed by an opposition between Mercury and Jupiter with Neptune as apex of the square. All three planets are in their own signs with Jupiter being retrograde. Mutable signs, being so flexible, usually end up stressed and anxious when under pressure. The Mercury-Jupiter opposition by itself could make us too sure of ourselves, cocky even, as the gift of the gab leads us to exaggerate or even sloppy as we tend to think we’re better than we actually are with this aspect. The Neptune apex adds confusion and misunderstandings since being clear or putting out all the information necessary will seem an arduous task.
A little bit of history:
Mercury in the Greek myth is associated with Hermes and he held an amazing number of roles here; thief, storyteller (aka liar), trickster, magician, craftsman, messenger of the gods, the god of boundaries, commerce, merchants, words and language among the many. He was the only god who had permission to travel freely between the Underworld and the heights of Olympus.
Mercury is so versatile that he can take on any of the archetypes represented by the other planets too and in this way he is also good at making deals or compromises and the house placement of Mercury in your chart will show where you’re good at this also.
Alan Leo’s description of Mercury from his book “The Art of Synthesis”
“A considerable portion of the correct judgement of a nativity is derived from the study of Mercury, its position, aspects and progress, the tendency of the mind being easily seen from the sign which Mercury occupies a birth.”
Leo A.  1949. “Chapter VI, Mercury the thinker.” In The Art of Synthesis pp 53-65. International Publishing Company, Edinburgh, UK