Understanding the true meaning in this sentence

Question

#25の制作は「ほぼオリジナルなので、まずは原作サイドで書くべし」と始まりました。
そしてできあがったきのこによる脚本モドキを前に頭を抱える制作陣。

It comes from this blog: http://www.typemoon.org/bbb/diary/log/201506.html

My translation: I began by thinking that #25's script was "mostly original, so I should write this as a side story to the original [the VN] story." And so I, Kinoko, was at my wits end trying to write something approximating a screenplay.

I would like you to give me your translation of such sentence.

I'm particularly interested in the reference to the script and how it's supposed to be almost original. Any reference to that script (and where it comes from) I might have neglected is most welcome.

Edit: My translation wasn't very literal. Another approach would be something like:

The production of episode 25 began with "since it's mostly original content, it should first be written by the original author". And then the production team clutching their heads at the completed so-called script by Kinoko.

The question is the same.

Answer 1

According to Wikipedia:

Fate/stay night テレビアニメ第2作
シリーズ構成、脚本はufotableスタッフが担当。奈須は全ての脚本会議に出席、ufotableが制作した脚本に奈須が加筆・修正を加える形で脚本制作監修を行った。
_{(※奈須 = きのこ)}

So きのこ was both the original author and scenario supervisor of this anime series. With this background, the sentence in question is interpreted as follows:

"I started creating Ep. 25, thinking I should firstly write as if I were just an original author (i.e., only from the original author's perspective)."

It means he intentionally and temporarily forgot about his job as the scenario supervisor of the anime. While he wrote the story of #25, he did not care much about how it would look like as an anime episode. As a result, what he made looked like a long ordinary novel, and it was not directly usable as the screenplay. That's why other staff were at a loss and had to trim much of what he wrote.

Note that this ～サイド does not mean a side story, but something like "～'s standpoint/perspective". 原作 is an original author. ～モドキ is "pseudo ～", "wannabe ～", "mock ～", "-oid", etc.