>>43827415>>43828129When the Anime Staff began production of the third movie, they had no idea what the plots of the Johto games were and didn't even have half the Johto roster.
Entei and the Unown were some of the handful of choices they were allowed to make a movie about, but they were only given vague concepts of the Pokemon. Like, "Entei is a fiery beast legendary" or "The unknown are super natural letters from the past that had some impact on older Pokemon civilization."
That's why they're so removed from their in-game counterparts. At least with Entei, he was an illusion, so it didn't really matter what they did with him. They went ham with Unown though, and even after their role in the games were revealed, the Anime hasn't ever retconned what they did with the Unown in the movie.
Some people think that the movie actually inspired their larger role in HGSS with the Arceus event in the Sinjoh ruins, as well as giving a way to tie myths from both reasons together, connecting the games. Which, also impacted the the anime movies around that time, having the Creation trio appearing in the Unown Realm.
Hopefully, whenever we get DPP remakes they'll expand further with the concept.