Imp's Mischief

The trick here is the color, not the effect. Redirecting a spell is the kind of thing blue does with Misdirection or Deflection, where the manipulation of the stack is part of the color's identity. Doing it in black demands a tax, and the tax is bespoke: you pay life equal to the redirected spell's mana value, so the bigger the threat you bend back at its caster, the deeper you dig into your own clock. That single line of life-loss is what keeps the effect honest in a color that is otherwise supposed to be buying its way around problems rather than answering them on the stack. The applications cut both ways. It saves your own creature from a removal spell by sending the kill onto something of theirs, it turns an opponent's burn into your offense by aiming their reach back at their face, and in older combo shells it functions as a counterspell for a counterspell, protecting a key spell by hijacking the answer aimed at it. The constraint that narrows all of this is "single target": a spell that hits multiple things, or none, is untouchable, so the card is a precise instrument rather than a catch-all. Black rarely gets to play on the stack at all, which is why this design has stuck around as the reference point for what a black-colored interaction spell can look like when it borrows blue's job and pays for it in the one currency black always has on hand.