The heck is that majin guy's magic? Making sharp squares? Not exactly a lot of detail on these spells...
That, my dear padawan, was the visible part of the spell "Death by Papercut".
It summons a number of trading game cards depending on the user's specification and limited by the user's total mana.
It then launches the cards at any available nonlethal surface on the target, doing minimal but still annoyingly painful damage.
The higher the obscurity/lack of adoption of the actual trading game, the higher the level of the spell and as a result, the more painful but less damaging the attack is.
In its second form, as depicted here, it can also be used as a physical barrier.
It's power is not in its actual sturdyness, but in its ability to confuse and mesmerise the onlooker, as they try to figure out the mechanics of the game, as the card flip around showing their face briefly to any onlooker foolish enough to actually pay attention.
A truly demonic spell indeed...