It's Black Heart Spiral! She can take on the form of the Emotion-a monster with a heart for a head- but in her general state she looks like this. A gigantic heart with eyes and teeth that crawls using the ventricles like tentacles.

There are more Emotions based on the seven deadly sins--epitome of human/animal emotions--and they differ in color but all have the same general build in heart and full form.

Black Heart's sin is Rage/anger/hate/etc.