It is in the differences in the morays...for instance, I acquired the jeweled moray because it had been housed in a LFS
disply tank for 5 years...its tankmate, a green moray, decided, (after being with it in the same tank for 3 years) that it looked like dinner. I bought it for a mere 20.00 as it didnt look too good. A couple weeks in a hospital tank and he was fine. Later, the same green moray, ate the head off (literally) of a large snowflake that was in the tank. Alot of eels can cohabitate quite nicely without incident. Snowflakes, Chainlink and Zebras for instance are pretty docile. Greens and Tesselata's have no tolerance for anything.
My yellow head fimbriated's are a bit aggressive, but only towards things other than eels at this point.
They would eat a lion, small ones for sure but large ones would more likely be harassed to death. Smaller lions are eaten head first and so the spines do not affect the eel. My fimbriated ate a small fuzzy lion. At least I assume that is what happened after the lion disappeared and the eel went off his feed for a week. And later history showing his aggression confirmed my theory.
Eel tanks are cool, but the reason I added other fish was the fact that quite frankly, eels can be boring....once they settle into rocks, you rarely see any activity except at feeding time. I have compromised with interesting inverts such as stars, cucumbers and urchins to supplement the tank for activity.