There are some decks where Tiana might really shine, but it probably isn't this one, especially when so many of your characters are meant to return to your hand
Locus of Creation (my personal favorite!), can propel you extremely fast in mana with its landfall trigger, and Omnath's Compleated form, Omnath, Locus of All, stockpiles mana as Black mana and also draws an extra card each turn, potentially adding even more mana
Assimilation Aegis Assimilation Aegis is less versatile than Detention Sphere but more proactive than just an answer and is one of the best control magic effects white gets access to
Most recently it was The Blue Spirit, and before that it was Hraesvelgr of the First Brood, and before that it was Renari, Merchant of Marvels, with Feywild Visitor as the deck's background enchantment
I wrote a document for those meetings entitled "What We Know, What We Don't, and What We Should" that applied those three points to every major character in the saga
Keep an eye on your coin purse