Arena Closer

s appear when a match of Domination, Tag, Mothership, or Survival is finished or when a server closes in Free For All, Maze, 2 Teams or 4 Teams. Its smaller version is playable in Sandbox, when using the \ key several times.

The purpose of Arena Closers is, as their name implies, to close the server; players killed by Arena Closers are then kicked from the server, then the server restarts when all players are killed off the arena. However, if the player manages to survive them (e.g. by activating God Mode on Sandbox), the player would still be kicked out from the server after a couple of minutes. Unlike getting killed by regular tanks, Dominators, Motherships, or Bosses, you will restart back at level 1 when you are killed by an Arena Closer only once. However, their levels are kept in Free For All, 2 Teams and 4 Teams. Arena Closers don’t have a health bar, so they cannot be killed. Their bullets do three times as much damage as an Annihilator.

Design
The standard Arena Closer features a large yellow circular base, with a cannon that is similar to the back of a Flank Guard. It is about as large as a Dominator, and the bullets it fires are about as large as an Annihilator’s bullet. In Sandbox it takes on a blue color, and is several times smaller than the average Arena Closer. The yellow variations’ color is same as the Square’s, Summoner’s, and neutral Dominator’s color.

Spawning
Several Arena Closers (with a maximum of 16) will spawn when a Domination or a Tag match is finished. In 2 Teams, 4 Teams, or in FFA, the Arena Closers appear when only a few people are in the server or when the game is being updated. In Maze when the server has been up for 5 hours. Arena Closers may spawn outside of the boundaries of the map, in which case they will immediately target a player and move inside.

Behavior
The Arena Closer’s priority: When they attack, they will shoot at the target while ramming into them. When all targets are dead or neutralized, their AI has no reason to continue to fire, so they’ll be spinning and slowly drifting in a random direction, just like regular Polygons.
 * The surviving Mothership (before game mode removal)
 * Any and all players still alive (in the order of initial proximity upon spawning and then upon each killed player)
 * Any non-neutral Dominators.
 * Bosses that are in team grey.

Stats
The Yellow Arena Closer has: In Sandbox mode, the playable Arena Closer has the health of a normal tank, but their bullets are still far more powerful than that of any other tank, approximately equal to a real Arena Closer.
 * Larger bullet size than an Annihilator.
 * Three times the Bullet Damage of the Hybrid.
 * (Old Arena Closer) An unknown amount of penetration (allegedly the same penetration as the health of a trap deployed by a Mega Trapper), and takes at most 2 hits to kill its target (any playable tank)
 * The Bullet Speed of a maxed Assassin.
 * The Movement Speed of Protectors.
 * The Reload of a maxed Reload of the Basic Tank.
 * Effectively infinite health, as it cannot take damage.
 * Complete resistance to Damage knockback because of god mode or a passive setting.
 * (Current Arena Closer) Infinite bullet penetration.

Miscellaneous
The Arena Closers aren’t targeted by the Protectors until the Arena Closers accidentally shoot or bump into them. The base itself has no effects on Arena Closers. Also the AI Dominators, Bosses and Crashers don’t target them. Their body and bullets can’t harm shapes, the neutral bullets will just go through them, and the Arena Closers themselves will just push them out of the way. The Arena Closers and their bullets can go through the Maze game mode’s walls. Additionally, Arena Closers can go through each other.

Playable Arena Closer

 * Weak Against: Dominators
 * Strong Against: Every normal class

As the Arena Closer
There is no real strategy to use when playing as the most powerful tank in the game. However, you must be vigilant when other Arena Closers are present in the server, as they are one of the few tanks who can easily defeat you. Outmaneuvering them is usually the best option, but in a perfect 1 versus 1 situation, the winner is usually the Arena Closer who gets the first hit.

Against the Arena Closer
Arena Closers in the Sandbox Mode can only be easily taken on by other Arena Closers. Other tanks with massive health pools, such as Dominators which may stand a chance as long as they are careful to stay far away. All other tanks cannot stand the power of the Arena Closer..

If it is distracted, with a Ranger / Stalker or Streamliner, you could have a few chances to kill them at range since you have better FoV. You also have a slight chance of Killing an AC with the Overlord when spreading your drones at the AC.

Real Arena Closer
Yellow Arena Closers are essentially invincible, so fighting them is not an option. Escaping is virtually impossible, as they are faster than the Fighter, Tri-Angle and Booster class, even with fully upgraded Reload and Movement Speed combined you could not escape from the Arena Closer. However, if all of the Arena Closers are stacked atop each other, then the bullet onslaught can be dodged. This is a very rare situation, as it is hard enough to stay alive that long.
 * Strong Against: Any tanks without god mode
 * Weak Against: None

Old Arena Closer
Old Yellow Arena Closers are essentially invincible like current Arena Closers, so fighting them would still be hard but you could slow them down by using the Triplet or Tank Bullet Spammers. You were also capable of running away from it by using level 8 Tank, Tri-Angle or Booster (all with maximum movement speed) because in an old version, Arena Closers were as small as our level 45 tanks. This would make an Old Arena Closer as fast as our tanks. They also did not do as much damage so it was possible to out penetrate them with large bullet spammer hoards or with Destroyer branch tanks.
 * Strong Against: Slow tanks, Low Penetration tanks
 * Weak Against: Fast tanks such as the Booster or Tri-Angle, Bullet Spammers such as the Triplet, Tanks with high penetration/damage such as the Hybrid

History

 * Despite their strength and speed, their name tag used to indicate that they’re only level 1.
 * On July 31, 2016, the Arena Closers’ spawn was delayed after the message, “Arena Closed: No players can join”.
 * The Arena Closer was the first AI-controlled tank in the game.
 * It was originally much easier to escape the Arena Closers, as both their Movement and Bullet Speed were much slower than they are today. Some were able to survive their onslaught with maxed out Movement Speed, Reload and Bullet Penetration.
 * They were buffed to their current strength and speed in the same update that added the Domination Gamemode.
 * They were buffed again to be a lot bigger, so they can deal Body Damage, and shoot bigger bullets that are a fraction larger than the size of an Annihilator’s bullet, making it harder to dodge them.
 * As of September 3rd, 2016, with the addition of Sandbox Mode, Arena Closers became playable tanks, but only in Sandbox.
 * Since September 6th, 2016, they now have scores, and when they kill the Bosses the notification doesn’t state anything about “an unnamed tank” anymore.
 * Since September 25th, 2016, the Arena Closers were able to pass through Maze walls.
 * In an update, Arena Closers were no longer pushed back by damage. During the same update, they were given unlimited bullet penetration.
 * (Domination mode only) When all player controlled tanks leave/die, they will attack the player-controlled Dominators.
 * Their score was indicated as 0.

Trivia

 * You can survive a single collision from an AC bullet in sandbox mode, cause it only deals 49 HP damage per collision.
 * If you are killed by an Arena Closer, you don’t actually go to a new server, you just enter the renewed version of the same server. This was probably meant to prevent the game from getting massive ping freezing from redundant servers.
 * When something is shot by an Arena Closer, it seems to get “thrown” to one side before it is killed because of the Arena Closer’s extreme bullet knockback.
 * Arena Closers may spawn outside of the regular map boundaries. However, upon spawning, they will move inside the map boundaries (since their AI will target a player inside the map, and will proceed to move towards them).
 * Before, they spawned in the center of the map.
 * Arena Closers sometimes merge with other Arena Closers because of their 100% knockback resistance.
 * As such, they are the only tanks that can move on top of each other.
 * There was previously a Bug where Arena Closers AI broke, making them slowly drift like Polygons even if there are players left.
 * In Sandbox, the Arena Closer is just after the Necromancer when you use the \ command. This is due to the Arena Closer being the last added tank when Diep.io was released, and the Necromancer being added next.
 * Base Protectors can pursue and attack Arena Closers. However, Protectors will die upon impacting their bullet or body.
 * It has become a game in itself to try and survive the barrage of the Arena Closers for as long as possible.
 * Previously, you can survive the Arena Closers in Sandbox mode by opening a Sandbox arena, playing it as someone else, leave as the host, wait ten minutes, and enter God Mode as the other player.
 * You used to be able to survive it with a team of Mega Trappers and Hybrids until they were buffed to have unlimited bullet penetration.
 * Arena Closers come from all sides of the entire map so it is advised to stay in the middle if the player wants to survive for as long as possible.
 * Arena Closers have the shortest and widest cannons apart from all the tanks. They used to have a longer barrel when they were smaller however.
 * These tanks shoot the largest bullets of all tanks in Diep.io. They used to shoot bullets that were slightly larger than a max level Tank.
 * Old Arena Closers actually resembled an assassin.
 * Old Arena Closers used to be as fast as a normal tank
 * It is possible to survive a single shot from an arena closer because they have infinite penetration, not damage. You can tell by how in sandbox, you can survive a hit from the Playable Arena Closer if you’re a Dominator.
 * Along with bosses, neutral Dominators, and Base Protectors, the Arena Closers are the only Al-Controlled things in Diep.io that can detect invisible tanks.
 * Arena Closers get the score of killed players, but it only displays in gamemodes that show scores, like FFA or 4 Teams.

Bugs
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Patched or Removed Bugs
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 * Sometimes, when the Arena Closes, the AI of the Arena Closers would glitch out, making them slowly drift like Polygons even if there are still players on the server.