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