Solar Eclipse

The Solar Eclipse is an event occurring only in Hardmode. It is announced at the beginning of a day with the message, "A solar eclipse is happening!", lasting from sunrise to sunset. During the Solar Eclipse the light will be only slightly brighter than at night and you can see the moon in front of the sun.

It is similar to a daytime, hardmode version of the Blood Moon, and should be treated as such.

Players wishing to avoid the creatures spawned by this event can easily do so by burrowing underground, which prevents Eclipse enemies from spawning altogether, or by staying inside a floating house, since only the Reapers can pass through walls and they have the same shortcomings as Wraiths, namely, they can only ascend when inside a block.

Content
All of these have high HP and high damage, and some of them have special features that make fighting them extremely hard. It is recommended to treat this event as a Boss fight mixed with an Invasion, since there will be large numbers of very tough and unusually agile enemies, most of which are resistant to knockback.

Strategy

 * Every enemy but the reapers and vampires use standard Fighter AI, (and even the same jump range as basic zombies and goblins,) and will walk into pits just like any other zombie. Lava pit traps will destroy the whole invasion force but the reapers.  Hence, the easiest way to nullify most of the threat is to dig a simple tunnel underneath a small lava pit on some leveled terrain. That allows players to simply focus on fighting the reapers alone, (which are rare enough that you rarely fight more than one at a time,) while collecting all the drops.
 * More advanced arenas involve putting the player in a floating room above where the reapers can reach, with lava pits and traps set to repeaters to kill off mobs, and a teleporter or two to get to loot-collection points or out of the safe room. Even without traps, a weapon that attacks through blocks, (Inferno Fork, Mushroom Spear, Nettle Burst, etc.,) allows players to ignore most of the threats.
 * If the player wishes to fight the solar eclipse enemies directly, it is best to fight in prepared terrain. Flat terrain is good against most of the enemies, forcing enemies to come at only two angles, but many players recommend a pair of mounds on either side of the player to cut down on the distance at which the Eyezor can attack.
 * The enemies have a relatively large amount of health, defense, and offense, so use top-tier weapons specifically good against crowds. This basically means either high-rate-of-fire, or piercing combined with good knockback. (Eyezors don't suffer knockback, however.)  This includes weapons like the Flamethrower, Leaf Blower, Chlorophyte Shotbow, Rainbow Gun, Paladin's Hammer, among others.
 * The high rate of enemy spawns makes getting a Dungeon Key Mold relatively more common. In building an arena, a player might swap out the tiles they surround themselves with in order to get a chance to spawn different molds.

Trivia

 * Some enemies seem to be based off old horror movie creatures. Vampire resembles Bram Stoker's Dracula and Frankenstein is Frankenstein's Monster. Swamp Thing is, well, Swamp Thing (from DC Comics). Reaper and Eyezor don't seem to have a basis in old Horror Movies though.
 * It is not a total solar eclipse. It is actually an annular ring eclipse, when the moon is not quite close enough in its orbit to cover the entire sun. The moon has a elliptical orbit around the Earth, being closer or farther in its orbit at times. The moon also revolves around Earth at a 5 degree plane, where as if it was at a 0 degree plane, you would have a Solar Eclipse every lunar month.
 * The music that plays during an eclipse is the 'Terraria 1.2 Update - Music Spoiler' that Red uploaded to his Youtube Channel 'Demilogic' (http://www.youtube.com/user/demilogic?feature=watch) on August 10, 2013.

History
(Not actually working despite Developer tweet.)