Idea Cube

Creatures attacking you have Entropy 1. (When
that creature deals combat damage to you, you search
your library for a spell, exile it, then shuffle.)

When a spell or ability controlled by an opponent
causes you to exile a spell from your library, copy
that spell. You may cast that copy without paying
its mana cost. If it's a permanent spell, the copy
gains haste and "At the beginning of the end step,
sacrifice this permanent."