

Players must complete The New Strange to access this game mode. The opposing faction of enemies encountered in each zone is also randomized on a per-zone basis. In order to advance through the zones, players must maintain efficiency by constantly killing enemies, then entering a conduit at the end of the zone's time limit in order to progress to the next. Players are limited to one large room from a random tileset in every zone.

The objective is similar to Survival missions, where players must last as long as possible by continuously killing hordes of increasingly difficult enemies, as quickly as possible.

Sanctuary Onslaught is an endless game mode introduced in Update 22.18 ().
