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