When Alina's Sun Summoner abilities first presented themselves in the Fold, they were regarded as a miracle. For the first time in living memory, someone who could destroy the Fold and unite Ravka had appeared, like a goddess out of a legend. But even as Ravkans anointed Alina a saint, there was a growing concern at the Little Palace that her abilities aren't strong enough. So, General Kirigan wanted to add an amplifier to her arsenal — but not just any amplifier: Kirigan wanted Morozova's Stag. But why is the Stag so important in Shadow and Bone? The answer lies in the same Ravkan mythology that foretold the Sun Summoner.
Warning: Spoilers for Shadow and Bone Season 1 follow. There's a popular fantasy series trope that begins with a reminder that, as time passes, memories become legend, then legend becomes myth. That's a salient point for those entering the Grishaverse to keep in mind. Ravkan tales tell that one day, a Grisha who can summon the sun will come and save them. These stories also speak of the Morozova beasts, animals imbued with great power by the legendary Grisha Ilya Morozova, also known as Sankt Ilya in Chains.
He created three beings that were powerful amplifiers: a Stag, a Rusalye (aka an Ice Dragon), and a Firebird (aka a Phoenix). A Grisha who took down even one of these creatures and possessed their bones to amplify themselves would be powerful beyond words.
That was part of General Kirigan's plan: Find someone who could track down the Stag — the easiest of these mythical beings to hunt — and kill it, then use its enormous antlers to create a necklace of power. Moreover, the Stag looked to have chosen Alina to bear his antlers. Images of the Stag have been coming to her, unbidden, ever since she was a child. The drawing she made of it was the one Kirigan passed around when commanding First Army trackers to find it.
Mal was always the best tracker of any group and decided to take up the charge, even as his superiors poo-pooed this mission as chasing fairy tales. He found the Stag, though at significant cost; his best friends were killed in an attack by the Fjerdians during the mission. When he finally made it to the Little Palace, he attempted to leverage his knowledge of the stag's location to see Alina. Instead, it nearly got him killed.
Luckily, Alina had already staged a self-rescue from Kirigan. When Mal tracked her down, the two set off to find the Stag, as she realized the Apparat was telling her she needed this power to destroy the Fold. Kirigan beat them to the punch, however. He killed the Stag as Alina stood entranced by it, seizing its power for himself and control of her abilities.
But the Apparat wasn't lying about the Stag's properties being something to bestow, not take. Alina's moment of triumph came when she realized the Stag never chose Kirigan. It chose her. But even with the necklace, it wasn't enough to destroy the Fold; it was only enough to rescue both herself and her compatriots and get them to West Ravka alive.
That the Stag's necklace isn't enough to destroy the Fold is a crucial point. There are two more of these creatures out there, and Alina needs more power. Will these creatures also choose her? And where can she find them? Hopefully, Shadow and Bone is renewed for Season 2 so the series can start answering those questions.