Here is the full list of all 22 DreamDasher achievements.
Achieve over 2,000 deaths
Achieve over 1000 deaths
Achieve over 400 deaths
Beat game on easy mode
Beat game on normal mode
Beat game on hard mode
Finish a speedrun
Beat the game on any difficulty
Beat game on nightmare mode
Beat the game with less than 42 deaths on Easy+ Difficulty
Beat the game with less than 100 deaths on Easy+ Difficulty
Beat the game with less than 200 deaths on Easy+ Difficulty
Beat the game with less than 400 deaths on Easy+ Difficulty
Beat the game in under 30 minutes on Easy+ Difficulty
Beat the game in under 60 minutes on Easy+ Difficulty
Beat the game in under 90 minutes on Easy+ Difficulty
Beat the game in under 2 hours on Easy+ Difficulty
Collected all the crystals in the game
Into the fire
Find the crystals
Discover the darkness
And so we begin