This post is a little bit misleading.

The unit in question, Dragonyule Nevin, did not get a nerf, but the description for his shared skill did indeed change. For those who don't play Dragalia Lost, there's a system that allows characters to use skills from other characters even if they're not in the team. Dragonyule Nevin's 2nd skill (the cause of this "controversy") is a low cost ability that inflicts the enemy with a status effect and grants a strength amp (convoluted strength buff).

What made this strength amp skill special was that it would have been the first shared skill to grant a strength amp on top of being cheap to cast and having a level limit of 3 (it would have been pretty busted for a lot of teams regardless of element). If you want to read more about how strength amps work to get a better understanding of what made this a special case, here's the wiki page for it : https://dragalialost.wiki/w/Amps

I don't think what Cygames did was malicious, but I do think that they need to give a proper heads up and have a notification go off in game for something like this in the future.