The Skull Stalkers are failed Stalkers and are basically the same as the Blood Suckler enemy. Due to them being based off of the Stalker, they can turn invisible until approached. This does make them dangerous as they can explode before Aya has a chance to deal with them. Just like Blood Sucklers, they are killed in a single attack regardless. Chain reactions are common for them and can cause damage to other enemies around them.