Crimson Balrogs spawn rate

If you had 400 cards you obviously would have had more then 15, cards transferred over if the background didnt change so most low lv mobs/nearly every boss stayed and of course the mobs that lv didnt change aqua road comes to mind

Do you ever give any accurate information?

Aqua road monsters changed levels: Jr. Seal in previous monster book vs. Jr. Seal after monster book and Old Squid vs. new squid

Also, cards carrying over was not based on being the same color. I had collected all the boss cards from that event a few anniversaries ago on my sister's hermit, and most if not all of them did not carry over. For example, Faust, both of which were green, did not carry over. While not an avid collector, my sister definitely had her share of monster cards, especially the easy to find lower ones. Strangely, orange mushroom and green mushroom, cards that are easy to find did not carry over. However, for the purpose of this thread, the crimson balrog card DID carry over. I was pretty sure it did because I remembered thinking about the hassle of hunting the crog card in the new book, just to realize I had it already, but I checked on my sister's hermit just in case, and it was there.

Same here.. I still remember the first time I killed a CRog.

I remember mine too. It was when I hit 120, and managed to level up and die at the same time, because I could only survive crog because of HB. Good times, good times.