Here is the full list of all 18 Almightree: The Last Dreamer achievements.
Collect your first Sunsphere
Do your first Plantsportation
Have your first death
Complete a stage with no safe block behind
Play a stage 3 times in a row
Get injured 9 times by dangerous plants in one stage
Complete 10 stages
Complete 20 stages
Complete 20 challenges
Complete 40 challenges
Score a total of 40000 through all stages
Score a total of 120000 through all stages
Complete 1 round of Local Speedrace
Complete 10 rounds of Local Speedrace
Complete 1 round of Online Speedrace
Complete 10 rounds of Online Speedrace
Win 5 rounds of Online Speedrace
Win 15 rounds of Online Speedrace