Good Bad Bugs / Terraria

Examples still "at large"

• Minimizing the program in a certain way causes it to run ridiculously fast in the background. This is handy if you want to park somewhere safe and wait for nightfall/daybreak, or if you've set up an automated monster-farming trap and want to wait for a bunch of Random Drops.
• Light Discs, the Dao of Pow, and the Shadowbeam Staff, if used in just the right way, can actually glitch through one-block-thick walls.
• After the 1.2 Big Update, it is possible for worldgen to create a Lihzahrd Temple in the Jungle with a messed-up layout that allows you entry into the Temple without having defeated Plantera and getting the Temple Key to unlock the door.
• After the 1.3 Big Update, it is possible for worldgen to accidentally generate a Granite or Marble Cave mini-biome that overlaps part of the Lihzahrd Temple, similarly allowing you to break sequence and enter it long before beating Plantera.
• An interesting and much-exploited collision detection/clipping/zipping bug that was introduced by the sloped blocks in the 1.2 Big Update has been dubbed the "HOIK". Yrimir has demonstrated this bug by slaying the Dungeon Guardian with a HOIK setup that allowed him to attack it with impunity while zipping around it in a circle. HOIK'ing also has it's uses for various mechanisms and wiring system. Word of God has confirmed that no specific efforts will be made to fix the hoik glitch.
• By placing three wooden platforms, hammering all three so they face downwards, then pressing down, it's possible to slip through any one block wide wall — including the door to the Jungle Temple. Summoning the Golem still requires Plantera to be defeated, however.
• The Lihzahrd altar can spawn directly below a low ceiling on world generation, which completely immobilizes the Golem's main body when summoned by the fact that the golem spawns directly above the altar and main body cannot move through rocks. Assuming you can still get a clear shot at the body in this state and damage it, the fight becomes laughably easy since it eliminates much of the need to dodge the main body's attacks, allowing you to pick off the body parts at your own pace.
• A more subtle one exists for fishing in single player. Turn auto-pause on and cast a line, then open the inventory, take a single item out of the inventory and right click to drop with the cursor in a place you would cast and then close the inventory. You'll not only toss the item but the short animation of discarding an item is the same as swinging a rod, causing two more lures to be cast into the water. This can be a great way to fish a lot of items in a short amount of in-game time and you can wind up catching multiple quest fish that could be stored for later.
• Due to a coding oversight, Truffle Worms in the 3DS version use the Worm AI, meaning that they'll dive at you out of the ground instead of running away on sight. As you might expect, this makes them trivially easy to catch. This glitch was also present on the mobile version, but has since been fixed there.
• Due to the way invulnerability frames are calculated, taking Scratch Damage would prevent you from taking damage from a much more serious hit. This does not apply to the Moon Lord, whose attacks use their own invulnerability frames
• Because of how the Slimy Saddle's bounce attack works, it's possible to become invulnerable by repeatedly bouncing on a Target Dummy using a solid block to hold yourself in place and then attack using a wall-penetrating weapon.
• Anybody who loves green (and even more so if they don't give much of a fuss about blue) will probably be pleased that Deep Sky Blue Paint turns most blocks a dark green, even though its regular variant functions without a problem on those same blocks.
• A pair of state-changing glitches involving the Bast statue and the Campfire produces what players called the Transmutation or Philosopher's Stone glitch, which allows players to create vast quantities of duplicated items through an Item ID transformation caused by the glitch.

Examples which have been "fixed"

• Prior to 1.1.1, trying to place a recorded music box on a table would duplicate the item by a massive amount, these boxes sell for two gold each.
• Like all bosses the Eater of Worlds flees if he kills the player and there are no other players nearby to challenge him. Prior to 1.0.6 the Eater of Worlds was considered slain when he fled complete with full drops, allowing you to run back to the battlefield and collect its loot.
• Early after the 1.2 Big Update, canny players were able to use Actuators to force Lihzahrd Bricks into the background, allowing access to the Lihzahrd Temple without beating Plantera and getting the Temple Key. This was soon fixed. Likewise, they used to be able to use a Teleporter to bypass the door. Both of these were 'fixed' by making it so that Teleporters and Actuators could not work in the Lizhard Temple biome until you defeat Plantera.
• Version 1.2.4 added some amusingly overpowered acceleration mechanics with the Minecart's physics, allowing players to accelerate their carts to such an insane velocity that they can either get sent flying thousands of blocks away, accidentally get noclipped through terrain blocks out to the middle of nowhere, or sometimes even deal thousands of points of damage to any enemies or bosses their minecarts run through when blazing away at such ludicrous speeds. This bug has been fixed as of 1.2.4.1, much to the disappointment of a number of players who were exploiting this trick.
• It was possible to fish up multiple Duke Fishrons in 1.2.4. Given that you pretty much have to be a certain brand of crazy to summon a second Duke while the first one's trying to tear you in half, hilarity most definitely ensued until it was fixed.
• With autopause turned on, you can swing your sword and pause in the middle of the animation to click a potion up from your inventory, unpausing will consume it, even if you have the Potion Sickness debuff that would have prevented you from consuming it in the first place. This was fixed by the time 1.2 rolled out.
• Fluid dynamics are completely broken, allowing you to create automated generators that create unlimited amounts of lava and water out of thin air, which in turn allows you to mine unlimited amounts of obsidian, which you can then turn into an unlimited number of obsidian skulls, which you can then sell for an unlimited amount of money. Basically, once you obtain a bucket of lava, your wealth is only limited by your patience. The core of the issue is how the game handles the flow of a liquid being split in two. A simple but effective "liquid multiplier" is a pyramid consisting of floating single blocks with space between them, so one block of liquid at the top flowing down gets split again and again and again. At the bottom all those fractions add up to much more than what you started with. It is basically taking advantage of the game code rounding out numbers where keeping precise track of everything is not needed for normal gameplay. This got fixed right around the same time the Bottomless Buckets were added to make infinite-fluid tricks a lot simpler.
• Prior to the Journey's End update, output pumps produced more liquid than what the associated input pump took in. While this made for easy liquid duplication and automated filling of fishing spots, it also made it very easy for waterfalls and moats to overflow.
• During the early phases of the Journey's End update, it's possible to duplicate shells with the clever use of platforms set in between grid blocks, then sell them off. This was quickly fixed.
• Phasing through shimmer rendered you invulnerable. People used teleporters and bubble blocks to infinitely phase through shimmer and let their summons kill the boss. This was popular while fighting the Empress of Light during the day, whose attacks were a One-Hit Kill during that time. Come 1.4.4.4, phasing through shimmer no longer renders you immune to bosses.