Here is the full list of all 21 DeathMetal achievements.
Finished Level #10 in Episode 4.
Finished Level #10 in Episode 3.
Unlocked Episode 4.
Finished Level #10 in Episode 2.
Unlocked Episode 3.
Collected tiny balls malus 10x.
Collected smaller paddle malus 10x.
Collected slow speed bonus 10x.
Finished Level #10 in Episode 1.
Collected extra life bonus 10x.
Collected fire bonus 10x.
Played with 4 balls at once.
Collected 100 bonuses total.
Collected bigger paddle bonus 10x.
Collected high speed malus 10x.
Unlocked Episode 2.
Collected split ball bonus 10x.
Collected big balls bonus 10x.
Collected magnetic bonus 10x.
Finished first level!
Played with 6 balls at once.