Here is the full list of all 25 Electric Zombies achievements.
Kill the fifth boss
Enter the fifth level
Kill the fourth boss
Enter the fourth level
Kill the third boss
Kill 1000 Zombies
Enter the third level
Kill the second boss
Use a burner on the 2nd level
Enter the second level
Kill the first boss
Kill 100 Zombies
Heal 10 times
Heal 1 time
Make a zombie fall into the abyss or fall there by yourself
Use a trap on the first level
Die 1 time
Kill 10 Zombies
Find a meds kit on some level
Enter the first level
Kill 10000 Zombies
Die 10 times
Die 100 times
Heal 100 times
Heal 1000 times