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Undertale Yellow’s broad plot was written before that lore drop existed. Hell, Undertale Yellow existed before that lore drop existed.
Humans being able to perform magic already existed through Glitchtale, and as much as I hate to acknowledge its existence, it was a pretty big AU in it’s heyday, and would’ve definitely influenced a lot of people.
If I made an AU focusing on the justice soul pre-10th anniversary stream there would be no questions about giving them the ability to shoot magic bullets. And everything else is either there for the plot or there because it’s cool. Dashing was there so that new attack types could be brought in that couldn’t be dodged with the base UT moveset, entering people’s memories is just a reference to when Frisk sort of does that in the Asriel fight and primarily serves to add further depth to Martlet’s and especially Ceroba’s characters while also filling in the blanks on major plot details in the case of the pacifist Ceroba fight.
So, no. Clover isn’t a powerful mage in a time when mages shouldn’t exist. They’re just a powerful mage.