Create outlines with black puffy paint
The primary use has always been Ancestral Recall as a quick way to move through the deck and pull ahead on cards, but there are great bombs (Gifts Ungiven, Mystical Tutor, Dig Through Time), draw (Gush, Thirst for Knowledge), and answers (Force of Will, Misdirection, Flusterstorm, and Hurkyl's Recall)
Take a look at the Source/Project64-core/N64System/Mips/Snapstation.cpp file in the Project64 fork linked above to see how this is described in code
It introduces both the new Illusion class and the Vanish keyword for the purposes of trickery and deceit
For anyone who hasnt tried something like this, counter manipulation is tons of fun, and it leaves a lot of room for customization and card exploration once youre done with the precon experience