If there are additional costs to cast a spell, or if the cost to cast a spell is increased by an effect (such as the one created by Thalia, Guardian of Thraben's ability), apply those increases before applying cost reductions
Sinister Concierge and Dogged Detective are excellent recursive creatures
Last year, you could walk into your local big-box, buy Mind Seize for $40 (assuming they were not sold out) and flip it to a buylist for $60
She doesnt even need to be attacking herself to make this happen, which is pretty bonkers
Katilda and Lier is the other not mentioned here, and its mostly because its a pretty forgettable card: flashback on instants and sorceries for casting Human spells
Bedrock Tortoise's ability doesn't actually change any creature's power