What does make Spike Spike? What is left if we take "dragon" and "assistant" away?

Background Pony #FAD0
So… If we have AU fanfic where Spike is not a dragon, nor Twilight’s assistant, how would one describe his personality while retaining his “essence”? It’s just that I read multiple AU fanfics about Spike, and it feels more like OC than Spike. If you change his colors and name, you would never even think main hero in those fanfics is Spike. So… is ‘ideal’ AU fanfic where you go “oh! that’s definitely Spike!” even possible, or his character was too inconsistent in the show for that? If yes, how one would do that?..
Background Pony #28E7
Snarky and sarcastic with a heart of gold. Greedy but at the same time very generous and loyal towards his friends. Probe to exaggeration while also being the occasional voice of reason to crazy Twilight. Honestly, the contrasts between when he’s the focus of an episode compared to when he’s not only make it glaringly more clear how inconsistently they write his character. Its extremely clear that they made Spike with the idea of him being Twilight’s other half for the earier seasons. Now that her character’s grown, Spike as the character he was originally designed to be is no longer needed and the writers are clearly struggling to find a narrative for him. Instead, they write him into inconsistent starring roles repeating the same lessons over and over again. If you were looking for a consistent Spike, safe to say there are two: Spike center stage and Spike the Assistant/straightman. As a whole, however, the only thing I can say is that he’s consistently inconsistent.
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