Seasonal

Seasonal is the fourth tier of rarities in BIS. Even though it is the same tier as Event, they are two different classifications. Seasonals reappear every season, while events are a one-time thing. You can tell them apart because Seasonals have "Seasonal | X season:" before the quote in their tooltip.

List of all known seasonals: List of current seasons for seasonals to appear:
 * Winter Boyo
 * Ghost Boyo
 * Sinister Boyo
 * ZomBoyo
 * Frozen Boyo
 * Halloween
 * Winter