Insta-kills are generally frowned upon, slightly less so if it involves hp. However, this is slightly less of an insta-kill than it is a "transforming" of the creature. The price seems about right, not too high to generate low usage, and not too low to be able to be splashed, well, anywhere really.
It also would improve the use of another underused Light shield:
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Replace the relics with Mercy Punishments.
Really, the only problem I see with this card is the name. I'm not a fan of names like these, though it is more the mechanic that matters with a card, not the theme/details. Good work!