Reaper Twins

The Reaper Twins is a hostile mob that spawns on the Death Day Event. It is a close cousin to the Night Reaper and Demon Reaper.

Spawning
Reaper Twins spawn naturally in the Overworld on the Death Day Event. They will despawn if the player get too far away from them or if the difficulty is set to Peaceful.

Reaper Twins can be spawned by using /summon nevermine.ReaperTwins.

Drops
Reaper Twins have a small chance to drop 2-4 Copper Coins at death. This cannot be increased with the Looting enchantment. They will also drop 3 XP orbs.

Behavior
Reaper Twins will pursue the player when the player gets 16 blocks or less from them. Reaper Twins will take the shortest possible path to get to the player (see image). Reaper Twins will always float on top of water, even if their target is below them.

Reaper Twins inflict a Blindness effect upon hitting the player that lasts for 1 second.

References/Sources
http://adventofascension.gamepedia.com/Reaper_Twins