This creature is attached to an extant single and solitary creature.
Any time this host creature is thought of, the Thought Creeper gets to attack the one thinking of it with the host creature’s usual (innate) attack method. But this damage is done mentally, and the attack can occur over any distance.
Referring to the creature indirectly is still thinking of it and so triggers an attack.
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The death of the host creature does not kill the Thought Creeper nor ends its effects. Thinking about the now-deceased host creature still causes mental attacks. Thinking of the Thought Creeper itself, as opposed to the physical host creature, allows the Creeper to attach itself to the person thinking of it. Multiple creatures may be infected this way (the #1 rule of Thought Creepers is you do not think about Thought Creepers, so clear your mind, Ray); it is how the Creeper reproduces.
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The Thought Creeper has no physical form whatsoever, has no stats, and may not itself be attacked or interacted with.