The phrase "zombie skulls" refers to the skulls or heads of undead creatures called zombies. It suggests a scary or fictional context where these creatures exist. Full definition
So, even though most people are still smashing zombies skulls on Dying Light, the question still arises «When is Dead Island 2 going to be released?! (xboxoneuk.com)
The game will pack in 30 songs (18 songs for Early Access, 30 for final release), half a dozen chapters of adventures and a community level editor that will allow any music to be played to the soothing rhythm of exploding zombie skulls. (shortpause.com)
The game is no doubt a zombie game but there is more to the game than just caving in zombies skulls. (gamegravy.com)