Crystalline Nautilus

The self-targeting clause is the whole story: this is a creature that sacrifices itself the moment any spell or ability points at it, no matter whose. That reads like raw downside, and largely it is one. A one-mana ping, a tap effect, even your own pump spell ends the creature outright. The design takes the most basic interaction in the game (point something at a permanent) and turns it into a kill switch that fires for either player. Where it gets interesting is what it forbids on your side. You cannot blink it, untap it, target it with protection, or pile a second Aura onto a host wearing it; whatever this thing is doing, it has to finish through combat alone, untouched. Cast for its bestow cost, the +4/+4 it grants comes welded to the same trigger, and the wording rewards a careful read: when the enchanted creature is targeted, you sacrifice the host, not the Nautilus. The Aura sloughs off and, because it is no longer attached, reverts to its 4/4 body on the battlefield. So removal pointed at a buffed attacker peels away the host but leaves you a creature, a quirk that softens the loss without making the card forgiving. The honest read is a permanent defined entirely by the act of being targeted, where the price of its hard immunity-by-suicide is that the same trigger answers an opponent's cheap spell or activated ability, and you forfeit every targeted trick of your own in the bargain.