Going for Hush? Say hello to the Book of Shadows. Upon use, it grants around 20 seconds of invincibility. Nothing crazy.

With the Book of Virtues, however, it spawns an indestructible wisp that can block all types of projectiles. The catch here is that contact damage (and beam attacks like brimstone) will kill it.

What ended up happening? I stocked up on soul hearts, got myself 8 Book of Shadows wisps, and was immune to all the projectiles Hush shot at me. What’s even better? Your wisps are immune to damage when you are immune to damage! These suckers deal 7 contact damage! Activate the Book of Shadows and rush into the enemy - the wisps will be invulnerable for those 20 seconds!

So there it is. The defensive and offensive capabilities of the Book of Shadows wisps. Also managed to kill Delirium on the same run. Fun times!