Unless you count Biorhythm, which really should be legal given the set-up required to kill someone
The idea is simple: Players take two packs of cards, put them together, and make an instantly-playable deck
It can also mean a spread of things like -X/-X, damage, destroy and non-targetted removal types
Like most Magic: The Gathering cards, the value of Opt depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Foundations Jumpstart)
Yet, there are some ways to go about casting this for a lot less than the actual costCounterlash, Magus of the Mind, Mind's Desire, Scholar of the Lost Trove, Sins of the Past, and Spelltwine all come to mind