Your first planeswalk brings you to Lorwyn. You can't shake the image of the horror in the mountain. You encounter an elf named Dwynen, who tells you their home is threatened. Inspired to help defend your elvish cousins, you join them on a hunt.
The Boggart Tribe's deck is a black-red Goblin tribal deck with sacrifice synergies. Several of their cards require sacrificing a Goblin for an effect, and some of the Goblins have triggered abilities when they die.
Despite the Goblins being generally small, the Boggart Tribe's deck has plenty of ways to remove Nissa's creatures or at least weaken them enough for the Goblins to defeat in combat.
Be aware of onboard tricks against the Boggart Tribe. With a sacrifice outlet like Facevaulter, they can sacrifice their creatures with death triggers like Hornet Harasser and get those effects at will.
Nissa gets two copies of a new creature, Dauntless Dourbark, starting in this mission, but unfortunately the Boggart Tribe has the perfect answer in the form of their three Boggart Loggers, which not only can't be blocked (due to them having forestwalk) but can sacrifice themselves to destroy Dauntless Dourbark. Note that the Dourbark's power and toughness listed in your hand will be one less than when you play it, since it will count itself once it's on the battlefield.