The way challenging works is a ready (untapped) character exerts and chooses an opposing exerted character to challenge, and then both cards compare their strength (attack) and willpower (defense) values to each other (meaning the attacker automatically gets hit back by the defender)
If the target creature is an illegal target as Sin's last ability tries to resolve, it won't resolve and none of its effects will happen
Some necessary backstory, and consider this your FF7 spoiler alert: After the burning of Nibelheim years before the primary events of the game, Zack and Cloud (along with Tifa) are gravely wounded in the confrontation with Sephiroth
While the lawsuit goes to great lengths to show the ways in which Lorcana resembles the as-yet-unreleased Upper Deck title, game mechanics, generally, are not protectable by copyright law
Still, thats a perfectly reasonable threat considering the utility of having it stapled to Zanarkand, Ancient Metropolis
Put a stun counter on that creature