Alright then, let's continue. First hints for the next batch;
#25: The original game in this series was named after the evil weapon, but this well-received sequel, and the series thereafter, was named after the good one. Guessed by Darashiva - SoulCalibur
#24: This game got two expansion packs, but the second one in reality doesn't actually have anything to do with the main theme and historical era of the main game.
#23: Features bosses that are named after musicians. Guessed by drbunnig - Super Mario Bros. 3
#22: In this game's predecessor, this unimportant side-character comments about how a certain item may make him "look a little tougher" when you give it to him. Who knew though that in this game, he'd become a lot tougher when he dons a similar, but much more powerful item. Guessed by Veknoid_Outcast - The Legend of Zelda: Majora's Mask
#21: At first the designers of this game had a male protagonist in mind. But after they noticed it got a little too much like a certain famous spy-movie franchise they changed the protagonist to female. Guessed by drbunnig - The Operative: No One Lives Forever