After Yubaba is told by Haku that something she loves is missing, she first checks the gold she has. However, once she realizes her son Boh is gone, she is so angry/worried, and the gold turns to mud.
Some fans argue over who did really did this. Some say that No-Face's gold is actually mud, but it seems like Yubaba, with her magical powers, turns the gold to mud herself during her anger. After all, why would the gold just turn to mud all of a sudden without magic? Even though No-Face "made" the gold, he wasn't in her office to transform it to mud, and we don't know if the other workers who got gold, like Lin, had their gold turned to mud as well, just because No-Face's possible "gold spell" broke and it all became mud.
So who really caused this?