any reason you're using Princess Lucrezia instead of Silver Myr, other than sheer style points?
Yes. I can't use ANY tappers that can tap to pay their own mana cost (if, say, their mana output is getting multiplied by a bazillion due to lots of
Mana Reflections). If I have anything like that in there, then I can just bounce it, replay it, tap it for lots of mana, which lets us bounce it again: infinite combo.
Princess Lucrezia was chosen due to the black mana in her cost. If she had been a monoblack creature that tapped for blue, that would have been fine too. (Ironically, all the creatures that can tap ONLY for mana that can't pay their own mana cost happened to be multicolour. Well...
Elves of Deep Shadow were an option, but that would have involved adding life-gain).
Good question, though, I really should add a paragraph or two explaining that.