When it enters the battlefield, it puts a creature or planeswalker spell from the stack back on either the top or bottom of the owners library
For example, Solphim, Mayhem Dominus and Fiery Emancipation will take a single Flame Rift, double its output from Solphim, Mayhem Dominus to 8 damage, then triple that via Fiery Emancipation to 24 damage to each opponent
The easiest battles to flip, Invasion of Gobakhan and Invasion of Zendikar, each enter play with three defense counters
Board wipes like Singularity Rupture can mill opponents for a significant amount
Wrap Up Thief of Sanity | Illustration by Igor Kieryluk As you can see, there's a big gap between casting the spells for free or just having to spend mana on a stolen spell
Hell, might as well throw Monologue Tax out there too since I'm talking about scaling