Solar Eclipse

Event
The Solar Eclipse is an event occurring only in Hardmode after Plantera has been defeated in the world. 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.

Unique Enemies
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 Invasion, since there will be large amounts of very tough and unusually agile enemies, most of which are resistant to knockback.

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 "fly" when inside a wall.

Tips
One effective strategy is to plant Tiki Torches to light up the area, and then use the Flamethrower to eliminate enemies. Since the flamethrower reduces forward movement, this will cause it to incinerate entire groups at once, making the Eyezor the only real threat.

Another useful setup is a Paladin's Hammer plus Titan Glove (or one of its derivates), since the extremely high speed and knockback allow the player to keep enemies away while dishing out serious punishment. This setup is more click-happy than the previous one though, and Eyezors are still a threat.

The Chlorophyte Shotbow may be your best friend if you are a ranged character. Even with standard Wooden Arrows, the multiple arrows fired per click all but neutralize the enemies' resistance to knockback, as well as dealing heavy damage.

NPCs

 * The Cyborg will sell Rocket IV