This is a similar situation to what happened for Set 3: Into the Inklands leaks, which happened on a much larger scale
I fully expect this to see play over a lot of the more common counterspells, at all power levels
A transforming double-faced card enters with its front face up by default, unless a spell or ability instructs you to put it onto the battlefield transformed or allows you to cast it transformed, in which case it enters with its back face up
Today we have the first batch of previews of spoiler season for the Final Fantasy set, our missing mechanics, cards for all 16 games including some legends from most of them, and more
This makes it easy to gain lore quickly out of the gate
You can cast a spell using flashback even if it was somehow put into your graveyard without having been cast