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
In fact, against decks that would usually outmaneuver green, Concordant Crossroads outright turns the tables
Illustrated by Vance Kovacs Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Legal Brawl Not Legal Legacy Legal Comp
With two cheap commanders in the Command Zone, you get to use Fierce Guardianship and Deflecting Swat for free, likely much sooner than your opponents, and much like Rograkh, you can offer up Silas to any cards that require a sacrifice to reap those rewards
But on the other hand, how much did we invest in this plan
This mana generators value depends on whether or not you have enough legendaries to maximize its mana income