Here is the full list of all 18 MEGAJUMP achievements.
Visited the bog
God confronted
Nice, weed achievement
gachiHYPER
Grey Duck spoken with
Jetstream Joe spoken with
Visited overworld. New challenges unlocked
Completed challenge run 1
Pogtruck visited
Main game beat in under 5 minutes
Bog route beat in under 7 minutes
Challenge level 1 beat in under 5 minutes and 30 seconds
Challenge level 2 beat in under X minutes
Challenge level 3 beat in under X minutes
Something has opened on a floor
You have beat the Tutorial Time Trial in under 50 seconds
Talked to Lei Wong within Challenge Level 2