The Summon Banshee is a conjuration effect from the Witchery mod. When performed, after about 30 seconds, a Banshee will be spawned. There is a small chance that a Poltergeist will also spawn. It can be performed by using a Wormwood, Condensed Fear, and Graveyard Dust on a Brazier, then lighting it with a Flint and Steel. The Brazier must have Altar power, which means it must be within 15 blocks of the Altar.