Sculk Creeper:

This mob has been taken over by the sculk most likely having escaped from the deep dark after being infected or quite possibly could have been infected by another infected surface mob. The creeper's original functionality is to walk up behind you, hiss and explode but with this one there are quite a few changes.

First off the head, this can open up 3x its original size almost like an Enderman reveling its sharp almost decapitation like teeth. When the head is closed you will notice the Sculk overgrowth on the head but with how the head sits it will not be obvious that the head can actually open. There is also a pupil in the right side of the creepers head giving it a chance to see unlike the warden itself.

Second off, the body itself. The torso has been cut in half reveling its ribs which is missing the very thing needed for it to explode like it normally would. So, this creature is in a constant hunt for TNT to fulfil the missing block within its chest. This lack of TNT will unfortunately for anyone coming across this will give the creeper an extra way to attack as the ribs can open and close themselves due to the sculks control over the body.

(There is an arm growth (bone) caused by the sculk but as of right now the creeper hasn't evolved enough to be able to use it so be thankful I didn't give it a god damn hook or claw arm that I was planning on adding. That would be amazing but no..)

This creature overall is more dangerous in a physical sense as it no longer makes any noise until after it kills its target. After it kills the target it'll make a warden like roar. If it manages to get TNT then the explosion caused by the creeper will spread the sculk in the area around it.