They did a good job with episode 0. It is a tough spot to try and adapt an arc in the middle of a story. So it was a smart move to do their best to give some background to the FGO story leading to Babylonia. But also making it an enjoyable episode beyond that. Bring the focus to Mash which is perfect. Through her we get to learn about the story, the setting, the stakes, and one of the main characters in this story.
Loli Mash going super badass awesome. I suppose you could summarize that sequence as "the servant we summoned for the demi-servant experiment didn't care to cooperate with us"
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Good focus on Mash, on Romani, and even a brief appearance by Da Vinci. The quick sequence near the end was both good to show the influences Mash has been exposed to...and to make me wish we could see some of these other arcs animated besides just the Camelot movie.