It’s the soundtrack and some DSO2 cosmetics that everyone who bought the game during early access got for free. They’re selling it to everyone else for $10.
Technically it’s DLC, not MTX as MTX almost always entails individual purchases of items, usually in-game. It’s more of a Collector’s Edition than anything. That no one seems to care about, even the people who detest predatory practices.
Do you mean the Mask of the Shapeshifter? That allows, once per long rest, to change appearance to another random character. Effectively a Disguise Self cast.
There’s also the dagger that’s 4-7 weapon. But I replaced that before I even dealt with the goblin camp. There’s so many magic items I wasn’t worried about it.
The biggest coup is the hat and cape. They offer no bonuses but they look so fly I’m probably never taking them off.