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