* Damage. Sigarda, Host of Herons is a 4/4 creature, so she can be killed by any source of 4 or more damage. This includes combat damage, burn spells, and abilities that deal damage.
* Exile. Sigarda, Host of Herons can also be killed by cards that exile her, such as Path to Exile or Swords to Plowshares. This is the most reliable way to kill Sigarda, as she cannot be regenerated or protected from exile.
* Sacrifice. Sigarda, Host of Herons can also be killed by cards that require her to be sacrificed, such as Altar of Dementia or Grave Pact. This can be a good option if you do not have any other way to kill her.
* Board Wipes. Sigarda, Host of Herons is a creature, so she can be killed by board wipes, such as Wrath of God or Damnation. This can be a good option if you have a lot of creatures in play, as it can take out Sigarda and her allies at the same time.