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