Guide:Arena

An Arena is generally a large enclosed area where the player can face a challenge in an environment they can control. It is generally designed to keep most enemies out while focusing on a Boss or other significant challenge.

Eye of Cthulhu
A highly recommended project for players who are about to summon their first boss. An arena for the Eye of Cthulhu should be large enough to dodge and maneuver around in, but small enough to seal off any enemies from wandering in and making the fight more difficult. A recommended size is just about the width of the screen.

Adding in a roof is also recommended to protect from airborne enemies and to keep retrievable ammunition from flying too far away. Making several large wooden platforms can make dodging simpler. As the fight will be at night, add torches to help visibility, including several in the ground underneath the arena.

Some players may choose to abolish the roof, and keep the Arena open to the sky. The reason being that there is a chance (however small) that Fallen Stars will hit the eye and deal 999 damage. This can make the fight far easier.

Eater of Worlds
Location is important for an arena of this sort. Specifically, the player must be in The Corruption to summon the Eater of Worlds, and moving too far away from The Corruption during the battle will cause it to flee. If there is corruption close to your base, then using it is recommended. Otherwise, artificial corruption using Corrupt Seeds and/or Ebonstone is necessary. An area of just corrupted dirt will work sufficiently to summon the Eater of Worlds.

The Eater of Worlds is, of course, a burrower, and will usually be offscreen and underground for much of the fight. A properly constructed arena can remove much of that advantage. Make the arena fairly tall, thin, and easily climbable with many wooden platforms. That way, you can not only see it coming, but this will force it to climb in a relatively straight line, leaving large portions of its body exposed, and vulnerable to piercing ammunition.

The above setup assumes you are using Worm Food to summon the Eater on the surface. If you are breaking Shadow Orbs, hollowing out an entire arena every third orb or escaping to a surface arena may not be practical; you should still modify the terrain around you to have a clear path of escape from the chamber where the Orb is located and ideally, easy access to a cleared space with good horizontal clearance and any hazardous terrain smoothed out or boarded over. Alternatively, if you have found a Magic Mirror, you can build a small bedroom at the top of your arena. Set it as your spawn point before descending into the chasms, then you can use the Mirror to return to the arena to fight after breaking every third Orb.

Skeletron
The entrance area to most dungeons can often be modified into a more desirable arena if needed. Most important is that you have room to dodge the hands, as well as enough vertical space to avoid getting trapped when Skeletron's head begins to spin. Walling the area off might also help exclude any minor enemies from joining the fight.

Ensuring the floor is nice and flat will also allow plenty of time to take advantage of the Skeletron's spinning attack, as its defense is set to 0 while using that attack. It may also be a good idea to bring along any Spiky Balls to set on the floor, if you have any from fighting the Goblin Army. When Skeletron begins his rolling attack, he'll roll right over them and take the full brunt of their damage.

Goblin Army
Location is important for this arena as well. The goblins will naturally target your initial spawn, that is, the center surface of the map. So no matter what you actually have there, that's the general area where you will encounter goblins when they arrive. You may as well prepare a proper greeting for them.

Make sure there are no NPCs in this area, as they will be attacked and possibly killed during the fight. Goblin Sorcerers' attacks go through walls and they can teleport indiscriminately, so the only defense is to make sure that your NPCs are not nearby.

Flatten out an area and make sure that there are no pits or jumps. Walls are not necessary, as during an invasion the newly spawned monsters are the target rather than a distraction. Make certain that any platforms or areas can be easily and quickly reached from anywhere else on the screen, since most players will be looking to quickly close in on casters with their melee weapons.

King Slime
Though this boss is particularly easy, and an arena probably isn't necessary, it's possible to exploit this creature's unwieldy size and movement pattern to create an area where it is impossible for the player to take damage during the fight. Create several "foxholes" poking up to the surface, large enough for the player to jump (and shoot) through but too small for the boss to travel in. Then connect them all with a tunnel.

Or you can build a 8 tall satellite with an open bottom and 4 layers of platforms and rapidly fire at him while the extra layers catch the extra blue slimes.

Wall of Flesh
The Wall of Flesh, more than probably any other boss, benefits from having an arena prepared before engaging. Even experienced players wishing for a quick fight should ensure that the path behind them is clear before summoning him. A full arena can speed up farming this boss, which can provide the player with several weapons and accessories that are valuable even late in the game.

The simplest arena is a long bridge of about 750 blocks with some space above it for the player to maneuver. Placing the player out of danger from falling into lava and ensuring that they can keep a steady pace of progression allows the fight to go quickly and smoothly. Players may also wish to place lights along the bridge, or place markers along the bridge at points where they've killed the WoF in the past.

The Destroyer
Your Eater of Worlds arena should also serve as an arena for fighting The Destroyer (However, moving the walls and ceiling in may protect you from of the Destroyer's lasers). The same types of visibility and movement are needed for both fights. The Destroyer does not need corruption present to be summoned.

The Twins
Building an arena for fighting the Twins can be a little tricky. Simply using Gravity Potions and fighting in the sky may be more effective. A long bridge may also work.

Skeletron Prime
Building an arena for fighting Skeletron Prime can be a little tricky. Simply using Gravity Potions and fighting in the sky may be more effective. A long bridge may also work.

Golem
An effective arena for the Golem would be to square out and level the room that the Lihzahrd Altar is in and use wings to fly around and dodge his attacks (mainly magic and ranged users). While exploring the Lihzahrd Dungeon, you can gather all the traps. Construct vertical pillars out of traps large enough for Golem but high enough for him to not get out on both sides of the altar. Finally line the ceiling with spike ball traps. After summoning Golem leave the enclosure and repeatedly activate traps to help fighting Golem (Be careful for the spiky ball traps, as they still hurt you)

Meteor Heads
Farming Meteor Heads can provide large amounts of coins. An "artificial" meteor can be created by placing exactly 50 meteorite in close proximity to each other. This can be done inside under controlled circumstances to farm these creatures. To deactivate the meteorite, removing only one piece is required. This method is not incredibly efficient as the Meteor Heads move very slowly.

Fire Imp
Fire Imps, as anyone who has fought one knows, teleport quickly and shoot fireballs that pass through walls. When they are hit once, they stop firing and pause at their present location for a number of seconds, leaving them vulnerable. Creating a long horizontal enclosed tunnel about 4 tiles high, with a good deal of empty space above and below, will assure that the Fire Imp will usually spawn within reach of the Vilethorn, which can attack through walls. The Vilethorn will take some time to kill the Imps due to their high defense; you can opt to use the Vilethorn just to stop the Imps from attacking, then wait for them to teleport within your tunnel (which will usually happen on the second or third teleport), so you can hit them with the Thorn Chakram, which will kill them very quickly.

Demon
Demons can be farmed in a similar way to Fire Imps, though it is important to remember that the Demon's projectiles can damage the player through one-block-thick walls, if you're in contact with that wall. In case Demons spawn below the platform you're standing on, you'll want to make that platform 2 tiles thick. Also, if Demons spawn below your tunnel, you will want to have solid ground or another platform built far below your tunnel to catch dropped loot (anything but lava). Demons will always fly as close to you as they can, putting them well within range of the Vilethorn, which will dispense with them rather quickly.