Back in October 2016, Insidious Will was a card which Magic the Gathering players were pretty excited about. Even though this spell costs 4 mana for a choice of three effects that typically each cost only two or three mana, the versatility of this card seemed to make it worth playing. With Baral, Chief of Compliance looking like he’d be a big part of Standard, it seemed to some people that Insidious Will was going to be a key part of Blue decks. This never happened, although Baral, who makes Instants and Sorceries you cast cost 1 less mana, is very good. Also, Baral is going to be tied to this card’s long term value, thanks to Insidious Will becoming a staple in his Commander decks.
Two of the effect choices on Insidious Will are the same effects as previous spell cards called Redirect and Twincast. These are cards that each cost two mana to cast, but being able to choose seems worth an extra price. The third choice is essentially Cancel, which is a three mana spell that counters any other spell. But, even though all these choices on one card in a control deck are a nice thing to have, it doesn’t appear on its surface to be worth the loss of efficiency in mana cost for effects that exist more cheaply on similar spells.
However, Baral, Chief of Compliance made Insidious Will actually playable, thanks to chipping off one colorless mana from Insidious Will’s mana cost. This turns Will into a sort of control Swiss Army knife spell. Naturally, Baral EDH decks typically have a copy of Insidious Will, and even in 2022, Baral is still among the more competitive Commanders in the format. He even proved so powerful that he was banned in Duel (1v1) Commander. So, clearly most demand for Insidious Will comes from EDH players. Baral is definitely the one who’s added this spell to his library the most, but he is hardly the only Commander that plays this versatile 4-mana instant. Many other spell-slinging Commanders, such as Deekah, Fractal Theorist and Melek, Izzet Paragon.
So, if it’s so useful in Commander, what’s made Insidious Will into a bulk rare? It simply never found relevance in the Standard format of the day. That’s partly because Baral rarely saw play in Standard, not because he wasn’t good, but because Control decks weren’t anywhere near the top of the format. This was the era of Copy Cat Combo and powerful Aggro decks, even in Blue/White. Baral would actually take off in Modern, where he would be a staple of Blue/Red Storm decks from 2017 through today.
Sadly, Insidious Will just was a bit too clunky for the much faster Modern format. Insidious Will would pop up in the odd Blue/Black Control list, Izzet Dynavolt deck, or even Simic Aggro shell. Some people considered trying to use Insidious Will to copy Approach of the Second Sun for a quick instant win. Unfortunately, that didn’t work rules wise because the second copy of Approach of the Second Sun had to be cast from the hand. The only other competitive play outside of Baral Duel Commander decks before his banning for Insidious Will was high-level sealed tournaments around the release of the Kaladesh set.
While Insidious Will is definitely an interesting card, its full value would never be realized in competitive play. Still, it’s a very useful spell for a variety of Commander decks, to the point where foils and stamped release promo versions are still valuable pick-ups. If you’re trying to build a strong collection of versatile spells for Commander, this is a strong one to add to your collection.