Solar Eclipse

Event
The Solar Eclipse is an event occurring only in Hardmode after any mechanical boss (The Destroyer, The Twins, Skeletron Prime) 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. If you have time, prepare the arena to include two short 'mounds', which will protect you from the Eyezor until it hits the top of the 'mounds' you have created, though this will allow the Reapers to have more cover as they move through the 'mounds.'

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 Mushroom Spear is also quite effective. The spinning mushrooms deal quite a lot of damage when the mobs run through them. All knockback bonuses are of use. Either trough reforging or by accessories like the Titan Glove.

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