Mark
Mark's crew makes it off Mars without Mark as they believe him to be dead. It's the biggest irony in the film and the catalyst for the story as Mark is, in fact, alive and he becomes their new mission - to get him off Mars alive and bring him home to Earth.
Space Pirate
Mark must resort to doing anything necessary in order to survive and attempt to find a way off Mars. Ironically, this causes him to be able to make decisions that under normal circumstances with his crew around he wouldn't be able to make - such as commandeering a space craft from another country. His maneuver technically makes him a pirate...a space pirate.
Funeral
Mindy has been surveying Mars with a satellite and finds images of the Hab with Mark in them and realizes Mark is alive. Ironically, NASA has already held a funeral for Mark and buried him.
Crop
Mark has figured out a way to grow potatoes on Mars which will allow him to survive longer. Ironically, there is an air leak from a small puncture and the airlock malfunctions and destroys all of Mark's efforts, leaving him even more uncertain of his survival.
Hermes
Sanders has rejected Rich's plan to send the Hermes back to Mars for Mark. Ironically, Henderson sends the plan to the crew of the Hermes before their arrival back on Earth allowing them to decide what to do. And, they choose to go back for Mark.
