Combat Mode, also known as PVP in Super Hero Life, is a mode coined in all Super Hero Life games to date.
When very first entering the game, the player will have the choice between Combat Mode or Roleplay Mode.
Combat Mode is for players who aren't interested in roleplaying. Instead they can use powers to fight and kill other players with their powers and weapons.
People can, and often will, roleplay in Combat Mode. This makes for an even more interesting form of roleplaying due to the fact that the player can fight villains/heroes instead of pretending to.
It all depends on the players' preference.