Here is the full list of all 149 Nightmare Reaper achievements.
Obtain 5 nightmare reapers
Obtain horse water
Sell 25 weapons
Get all bonuses in a level
Obtain reflection
Break 250 clutter objects
Obtain 100 headshot kills
Obtain V
Obtain a 15x combo
Complete hollow stone
Obtain 50000 gold
Get all secrets in a level
Obtain 100 treasures
Complete 5 random events
Break 100 clutter objects
Kill 100 enemies
Wake up prematurely
Sell 10 weapons
Get all treasures in a level
Buy a skill from the tree
Obtain a rare weapon
Obtain 20 headshot kills
get all kills in a level
Obtain 10000 gold
Obtain an uncommon weapon
Obtain nightmare reaper
Obtain 20 treasures
Kill 30 enemies
Obtain a 5x combo
Obtain a level 2 weapon
Obtain a 25x combo
Obtain a 35x combo
Reach bynnyhop max speed
Do 20 rocket jumps
Kick 50 enemies to death
50 high falls into water
Douse yourself 50 times
Buy 10 skills from the tree
Buy 25 skills from the tree
Buy 50 skills from the tree
Buy 75 skills from the tree
Buy 100 skills from the tree
Buy 125 skills from the tree
Buy all skills from world 1
Buy all skills from world 2
Buy all skills from world 3
Buy all skills from world 4
Buy all skills from world 5
Buy all skills from world 6
Buy all skills from world 7
Buy all skills from world 8
Complete spore pit
Complete immemorial woods
Complete forsaken village
Complete sulfuric mines
Complete disavowed town
Complete putrid sewers
Complete drudge village
Complete gloom mansion
complete the descent
Obtain a legendary weapon
Obtain a level 3 weapon
Sell 50 weapons
Sell 500 weapons
Kill 500 enemies
Kill 5000 enemies
Obtain 1000 treasures
Obtain 10000 treasures
Obtain 150000 gold
Obtain 1000000 gold
Break 2500 clutter objects
Break 10000 clutter objects
Obtain 5 Vs
Obtain 20 Vs
Obtain 500 Vs
Obtain 5 horse waters
Obtain 20 horse waters
Obtain 500 horse waters
Obtain 5 reflections
Obtain 20 reflections
Obtain 500 reflections
Obtain 20 nightmare reapers
Obtain 500 nightmare reapers
Obtain 1000 headshot kills
Obtain 10000 headshot kills
Kill 3 enemies with one bullet
Complete 15 random events
Complete 75 random events
Complete 250 random events
Complete carnage way
Complete tower of toil
Complete gardens of woe
Complete murky docks
Complete vermilion princess
Complete rust works
Complete void beneath
Complete gibbs medical center
Complete boulder penitentiary
Complete 5 levels with pills
Complete 15 levels with pills
Complete 45 levels with pills
Complete 135 levels with pills
Complete 405 levels with pills
Find everything in the hospital
Get the sacrifice ending
Get the control ending
Complete the wasteland
Complete fields of death
Complete moon terror
Complete sorcerer's mansion
Complete the empty
Complete crushing depths
Complete buried ruins
Complete blood and brimstone
Complete the flesh pits
Sell a weapon for 1000000
Accept 5 merchant offers
Have a carried barrel explode
Start a level with no weapon
Kick a boss
Burn freeze and shock an enemy
Lose 2000 life as blood ammo
Pickup a weapon after death
Change a stat to +2 attack
Change a stat to blood ammo
Complete a level with 20 toxicity
Complete a level with 100 toxicity
Complete a level with 250 toxicity
Obtain 20000 jade
Obtain 60000 jade
Obtain 240000 jade
Obtain 1000000 jade
Buy 10 jade upgrades
Buy 50 jade upgrades
Buy 100 jade upgrades
Buy 180 jade upgrades
Reach round 10 in an arena
Reach round 50 in an arena
Reach round 100 in an arena
Unlock 2 arenas
Unlock 5 arenas
Unlock 8 arenas
Have a pet with 2 skills
Have 2 pets
Unlock all pets
Unlock all pet skills
Reach New game+ 1
Reach New game+ 2
Reach New game+ 3