Reapers behave in a similar manner to Wraiths, but they have higher stats. They move significantly faster than Wraiths, and with the higher spawn rate of the Solar Eclipse, they often attack from multiple directions at once.
They are fairly vulnerable to knockback. Like many creatures that pass through blocks, they do not take damage from lava. Furthermore, weapons that generally do not harm enemies through blocks, like most melee weapons, will damage them.
Notes
Similar to Wraiths, they are incapable of ascending more than a few tiles above solid blocks.
Tips
Standing on a platform several tiles above the ground or using wings or Rocket Boots (or its upgrades) allows players to shoot down upon them with impunity if they are going to be surrounded.
The Static Hook, obtainable from the Steampunker, provides for safe means of combating Reapers by simply remaining stationary above the ground in an open area and attacking downwards. Note that this strategy opens the player to attack from flying Vampires, and leaves them stationary for an Eyezor to attack.
Similar to Eyezor, the Reaper does not allude to a specific horror movie, instead being a reference to the Grim Reaper.[1]
The sound the Reaper makes might be a reference to the series of action-adventure video games Legacy of Kain, when Raziel swings the spectral Soul Reaver blade.