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