You have been chosen the opportunity to exit your own universe and explore the surrounding Totality as much as you wish. As for what you will do with this opportunity, that remains up to you. Will you bring heroism and love to the surrounding cosmos or will you enslave and destroy everything you come across? Will you defend the innocents or slay the defenders? Will you simply watch and observe? Will you seek to rule Totality single handedly?
The catch is this, all you get is limitless planeswalking and one power of your choice. Choose wisely.
Note: No powers which allow true omnipotence, true omniscience, or true omnipresence.