They remain still in their assigned houses at night and during events. Town NPCs generally walk around during the day. These reductions are usually overridden by events like Blood Moons or Goblin Invasions, during which spawn rates return to normal or are elevated, and enemies will once again attack players and NPCs in the area. Players tend to utilize this effect by building large structures ( towns or bases) with several integrated houses, to serve as their safe haven. With 3 or more town NPCs nearby, enemies generally stop spawning on or near the visible screen altogether (unless in Expert Mode or Master Mode ). Town NPCs that have moved into houses reduce enemy spawn rates in the area, an effect that increases the more of them are present. They move into structures the player must provide, known as houses, which are generally required for town NPCs to remain available. Most NPCs are town NPCs, appearing after various milestones are achieved in game advancement. Some NPCs also have other options that perform other functions. They sell items to players in exchange for coins, and can be sold items by a player to obtain coins. Most NPCs are vendors, displaying a shop inventory when the " Shop" option is selected. Standing near an NPC and pressing the ⚷ Open / Activate button on it will open a dialogue window with one or more options for the player to select. NPCs are friendly automated non-player characters that provide services to players. For a complete list of NPC names, see NPC names.