If multiple creatures are put into their owners' graveyards at the same time (due to combat damage or Planar Cleansing, for example), Agyrem's first two abilities trigger that many times. At the beginning of the next end step, the player whose turn it is at that time puts all of their Agyrem delayed triggered abilities on the stack in any order, then each other player in turn order does the same. The last ability put on the stack is the first one that resolves. The creatures are returned one at a time.