I've been unsure for a while how to use the tag Madou Monogatari. For those unfamiliar Madou Monogatari is the original dungeon crawler series that PuyoPuyo is a spin-off of. Originally created by a company named Compile the rights to the characters in those games as well as the Puyo Puyo IP was sold to SEGA resulting in the Fever iteration of the franchise and the start of the drastic style shift.
Anyway history lesson aside, everything currently in the Madou Monogatari tag also currently tagged as Puyo Puyo. All of the older posts in the Madou Monogatari tag are just PuyoPuyo from the compile era. post #1016406 is Puyo Puyo Sun art, or solo pictures of Arle, Schezo, Draco with nothing about them relating to Madou: post #331173 post #213668 post #1428827
The only image in the tag explicitly relating to Madou I could even find is post #716528 which is an anniversary picture.
So, should this tag be used for any characters who showed up in it first? EVERY single character in these games was later used in Puyo Puyo, there is not a single one who didn't go on to appear in an entry. That would be major characters like Arle getting the tag always. Should it be used for older designs of characters? A lot of the "classic" Arle on this site is using a design that appeared first in older Compile Puyo titles, but post #6144393 and post #5951823 both use designs that were actually in Madou titles. This option would take the tag down to sub-100 probably.
Worth noting that Compile did eventually make more Madou Monogatari titles after they sold the rights to SEGA Sei Madou Monogatari which is in not implied to the main tag currently and has nothing to do with Puyo.
Updated