Terraria is a 2D sandbox game with gameplay that revolves around exploration, building, crafting, combat, survival, and mining, playable in both single-player and multiplayer modes. The game has a 2D sprite tile-based graphical style reminiscent of the 16-bit sprites found on the SNES. The game is noted for its classic exploration-adventure style of gameplay, similar to games such as the Metroid series and Minecraft.
The game starts in a procedurally generated world, with players starting out with basic tools and a non-player character (NPC) guide to get them started and bring their attention to aspects of the game and progression. The game's world is made up of several layers of tiles that players can interact with and modify. Many resources, such as metal ores, can be found while exploring caves. Players begin with low health and mana, which can be increased by finding and crafting specific items. Some resources may only be found in specific areas of the map, stored in common and rare containers, or dropped by certain enemies. Players use resources to craft new items and equipment. Different recipes require different resources and crafting stations. Several items in Terraria create complex crafting trees involving a large amount of items to create a single powerful piece of equipment.
Players have the option to customize their character's appearance when creating a new character, and in-game by visiting the Stylist NPC or the Clothier NPC. Along with that, players can obtain vanity items, which are special armor pieces and accessories with only a cosmetic effect, and dyes to change the color of equipped armor or accessories. Characters have three inventory slots for armor to be equipped, and several inventory slots for various accessories to provide a boost to a player's statistics, such as wings or water walking boots, as well as vanity slots for all of them, allowing them to be hidden behind cosmetics while retaining their effects. Much like most Terraria items, armor and accessories can be crafted, found around the world, and obtained from defeating bosses.
Players can encounter many different types of enemies in Terraria, the occurrence of which depends on several factors including time, location, and random events. The game features an open-ended class system, primarily divided into melee, ranged, magic and summoner classes. Players may also battle bosses that utilize a number of different combat mechanics and can drop rare and valuable items. Bosses are summoned by using certain items or when certain criteria are met. The defeat of some bosses is directly tied to in-game progression, while others remain optional. Defeating the Wall of Flesh boss advances the game into "hardmode", which adds many new enemies throughout the world, as well as new NPCs and items. Like bosses, players can battle special enemies and mini bosses during invasions, in which enemies appear constantly and they either must be defeated or a certain amount of time must pass before the event ends. Terraria also features seasonal events which activate during certain periods of the real world calendar year, adding new enemies and content.
By completing specific goals, such as defeating a boss or obtaining a certain item, players can attract NPCs to occupy structures or rooms they have built, such as a merchant, nurse, or wizard. Some NPCs can be acquired by finding them throughout the world and will then reside in player-created houses after being rescued. Players may then buy or sell items and certain services from NPCs with coins obtained from defeating enemies and bosses. The game features many different biomes and areas, which are each home to a unique set of enemies and challenges. The Corruption, Crimson, and the hardmode-exclusive Hallow, will expand by slowly overtaking and converting nearby blocks. NPCs prefer to be around certain biomes and with certain other NPCs, and will raise and lower their prices and sell special items depending on if they are sufficiently happy.
"Expert" and "Master mode" are difficulty modes that increase the challenge of the game in exchange for some exclusive items. "Journey" mode allows players to duplicate items, adjust the world's difficulty, and control weather and time at will while playing.
Terraria has support for mods, which is facilitated by the third-party tModLoader. It later received official support when it was released as free downloadable content alongside the "Journey's End" update on Steam in 2020. Mods for Terraria vary widely in their scope, content, and purpose. Some, such as Thorium and Calamity, add new content to the game, including new bosses, weapons, and biomes. Others, such as Overhaul, rework the mechanics of the game to provide players with a different experience. And additional ones, such as Recipe Browser, Veinminer, and Fargo's Mutant Mod, aim to improve quality of life by streamlining parts of the game.
