Capture the Gem
Capture the Gem, commonly abbreviated as CTG (sometimes stylised as CtG), is a Player vs. Player gamemode based on the popular game Capture the Flag. Major differences between the two games are that Capture the Gem uses Large Gems instead of flags, and that players are usually given around 15 minutes of "preparation time" to collect materials and build base defences. CTG is generally played as a 4v4 gamemode, though games as small as 1v1 and as large as 20v20 are possible. Capture the Gem is typically played using mediumcore characters, although any -core can be used since Large Gems always drop on death.
Capture the Gem is generally attributed to being created by Miles from OdysseyGamez in July 2011, and the first mention of CTG was within OdysseyGamez' video uploaded on July 20th, 2011. A second CTG ruleset appeared around November 2011 when Lewis from PsiSyndicate uploaded a video explaining the rules of CTG. This video sparked a conflict between Odyssey and Psi which lasted some time, but eventually subsided. Although the Psi ruleset is still known, since the channel quit Terraria in mid-2012, it has not been played.
Capture the Gem is played on a randomly generated map (usually medium or large in size) which then has two bases built East and West from the center point, two chests containing the Large Gems built some distance from the bases, and a center point, which is generally either coloured bricks or a small structure. Maps created are usually chosen to maximise fairness, although total fairness is almost impossible to attain due to the random nature of map generation. As a general rule of thumb, maps created or used within CTG should contain at least one natural cave for each team (excluding ice caves due to their lack of ores), have bases which are similar in height to one another, and have either high or low ground at the middle; any innate advantages such as one side being much higher than another should be avoided.
The object of the game is to collect as many materials as possible by caving and gathering materials such as wood on the surface during the preparation time (or phase), and then capture your opponent's gem after preparation time is over (in a phase sometimes referred to as the attack phase). Teams can make it harder to capture one another's gem by building base defences, usually consisting of either large dirt, sand, or wood structures which surround the gem chest or by building outward defences such as towers. Teams are encouraged to be creative with defences, and so defensive tactics occasionally include creating decoy chests, tricking the opponent into falling down a pitfall trap, and forcing the opponent into difficult situations to make it easier for a team to kill them.
The rules of Capture the Gem are relatively simply, and serve to ban imbalanced tactics or items which make games too easy, or fix the meta in a single position. The most recent large rules update was on October 28th, 2013 when OdysseyGamez released an updated rules video, some years after their first one.
Bases are typically 600ft from the centre of the map, and your chest will typically be 150ft from your base. Red Team is always on the right, and Blue Team is always on the left. The Preparation Time allocated is typically 15 minutes long. Any time the map begins to get dark, the host of the game should set the time to noon, ensuring all players have ample lighting and are not attacked by zombies or eyes.
- Join all CtG games as a new mediumcore character.
- Upon joining, wait for the host to teleport you - do not begin running around collecting items, and do not turn on PvP.
- After you have been teleported, join your assigned team colour, turn on PvP, and set your bed. Do not leave your house and wait for the host to announce that the game has begun.
 Preparation Time
- Do not cross or PvP across the center point during preparation time.
- No items are banned at this point in the game, so use them (outlined below) before preparation time is over to ensure you receive their bonus.
- You must not alter your gem chest in any way, including moving the gem inside the chest or moving the chest itself. You may, however, use the chest for storage.
- You must not place any blocks not mineable with a Copper Pickaxe at any time throughout the game. Furthermore, you may not surround your chest with lava (although lava can be used offensively).
- You should do your best to avoid getting any NPCs. If an NPC does spawn, you must not use them.
 After Preparation
- You cannot use any of the banned items at this point in the game UNLESS you are using them in a way that will not interfere with your enemy (e.g. killing a slime or collecting some ore).
- If/when you reach your opponent's base, you cannot destroy their bed, destroy their house, or trap them in spawn using blocks or lava.
- You cannot intentionally move your spawn point at any point during the game, including creating another bed or setting your bed at your opponent's bed.
- If you successfully get your opponent's gem, you must return to base as quickly as possible (you shouldn't spawn kill enemies for fun, for example).
- When you have the gem, you are not allowed to go underground with it.
- If you found a Magic Mirror in preparation time, you are not allowed to use it in conjunction with the gem to teleport instantly back to base.
- If the enemy team is attempting to get your gem, you are not allowed to access the chest to intentionally stop them from accessing it.
 Banned Items
Within preparation time, it is common to see two players caving (for speed and safety), one player creating the base chest defence, and another player either collecting surface materials for the defence builder to use or creating arrows. Although 15 minutes seems like a decent amount of time, due to the number of tasks that need to be done, teams can often find themselves defenceless if they have bad time management. Good teams strike a balance between offence and defence, as well as having multiple skilled team members who can each do their chosen/given tasks to a high level.
After preparation time, teams can choose to rush one another if they believe the other team isn't prepared, or they can choose to remain defensive until one team forces the other into combat. Common offensive tactics include skybridging and tunneling, and the most common fighting tactic is to "arrow spam", where a team will fire as many arrows as possible at an enemy in order to suppress and kill them. Other tactics can include attempting to get at least one hook and using swords (dealing more damage that bows and negating knockback with the hook), or attempting to backdoor an enemy team by sending one or multiple teammates into their base undetected in order to capture the gem without the enemy knowing.
Psi CTG, created by Lewis from the PsiSyndicate is one of the main variants on default (Odyssey) CTG, however, it is no longer regularly played since PsiSyndicate quit playing Terraria. The rules differ from the Odyssey ruleset greatly, and introduce mechanics such as receiving starter items at the beginning of the game (often pickaxes, dart traps, wire, and hooks), as well as encouraging much faster paced gameplay due to the addition of high-tier pickaxes and hooks. The game was not played during noon, and instead featured a full day/night cycle; it was only after the first night had passed that teams could attack one another, however, teams could still cross the center point previous to this. Base defence was characterised by the extensive use of traps, although "backdoor" gameplay was removed as a team must announce when they take an opponent's gem.
Another variant of CTG is Softcore CTG, where players are able to take bigger risks without punishment of losing all of their items. It allows for much quicker gameplay, however, it eliminates many of the tactical nuances which is often considered to be the core element of CTG.
Some players may also divulge in playing intentionally imbalanced CTG matches, such as 1v4, 4v8, 6v12, etc. This is to increase difficulty for the team with less players (which is usually "stacked", meaning it has many seasoned/veteran players on the team). Imbalanced games can be used for practice for competitive CTG players or teams who require both teamwork and individual ability in order to win matches.
Due to the competitive nature of CTG, it can also be played competitively in matches (one team vs. another team) and in tournaments.
 Gem Wars: Reddit CTG Tournament
By far the largest Tournament of its kind, Gem Wars is a CTG Tournament created in partnership between creators of CTG, OdysseyGamez, and the Terraria subreddit. Gem Wars is currently on its first iteration, and is being organised chiefly by Neszy and Aeroblop. Various Terraria YouTube Channels bound together in order to both play and endorse Gem Wars, with videos being produced from Yrimir, TerrariaHelp and ChippyGaming, and YouTubers such as HERO and Pedguin taking part in the Tournament.
Gem Wars contains a base pool of 64 teams and is single elimination until the Quarterfinals, where it turns into double elimination. The full bracket can be found here.