User blog comment:Crispycol/*Gasp* Roster revealed?!!/@comment-6137196-20140501135908/@comment-24943758-20140515054452

How's this, AnimaShaun? With the exception of the original Metroid (and it could be argued that the room was too small in that game), all battles with Ridley dealt with him primarily flying, and almost never landing on the ground (and even then not staying on the ground for too long). Having a character like that in the roster would almost undeniably force Ridley to be grounded, which is not what Ridley's fight style is like. If he were to remain flight-heavy, he'd be a massive pain to kill in any way whatsoever.

In order for Ridley to keep his traditional flight-heavy fighting style AND make it into the game, he'd have to be non-playable; ergo, a stage boss.