Clown Zombies are zombies originally exclusive to SAS: Zombie Assault 2 Insane Asylum. They are extremely fast and have high health. When they approach you their head will expand and explode, dealing huge amounts of damage, depending on how close you were and, killing the clown in the proccess. When spawned, you will hear the creepy sound of laughter. The Premium Temporal Displacement Armour is an effective way to block a potentially deadly blow from these zombies, though don't rely on it too much, as it won't work sometimes. The Witness the Fitness skill will also help you endure these fatal blasts.
In SAS Zombie Assault Tower Defense, there are Clown-like enemies. Like the Clowns from Insane Asylum, they will blow apart, damaging turrets and SAS troops. However, they appear to only do this when killed, and don't seem to actively seek out turrets and troops. They also appear to be robotic.