I remember watching some videos of this Musou version and as far as I searched it again a few days ago, I could only find 1 lance video and as I saw him fight I noticed that I used to try it similarly, but yet even Forest hasn't a video of this solo fight, I can only say that this fight is nearly impossible to be done solo using lance, there are two major problems, the monster has a lot of hard to evade attacks alongside with its high mobility against the lack of attack chances the lance get, so with this problem and the time limit of 10min for the true slay, it's nearly impossible.
At least it is a nice fight and it has a great BGM.
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Credits:
Intro animation created by Aronixz: https://www.youtube.com/c/AronixzAnimations/featured
Intro edition and song by my friend Rodrigo: http://www.linkedin.com/in/rodrigo-mulinario-ramos-76288115b/