Pokemon GO tends to rotate which Raid Bosses are currently available to players at a time, with each new rotating bringing a different set of encounters for which Trainers will need to properly prepare in order to gain the most benefits. Mega Raids, in particular, are some of the most difficult to go up against, as the sheer power of Mega Evolutions is much greater than that of an average Pokemon, often pairing them with improved stats or special moves.