This was one of my favorite cards when I played Yennett, Cryptic Sovereign, and its one of my favorite cards in this deck
However, you'll have to be careful with managing her dark side
The code is on Github and I'm going to talk about how it works and what I learned
Please note that XLHQ versions of cards are only showed in the zoom view, regular card pictures are still used (LQ/HQ, depending on what you're using) on the battlefield and elsewhere in the game because XLHQ art is significantly more taxing in memory consumption (and in addition to that, XLHQ card borders are not cropped the way Forge expects them in order to show them properly on the battlefield anyway)
Unlike Geralf Messengers first ability, the second one goes onto the stack and may be countered by related spells and abilities
People will frequently cast multiple spells per turn, so you are looking at significant Treasure gain from his card, which is just all around strong