Day 99, 12:00, for 12 hours: 107 zombies at ×21 health and ×24 attack.
Part of Endless tier 20, day 4 of 5.
When it ends: 
All-Purpose Strengthener
Fine Sheet Metal
Scrap Metal
Cold Cuts
Mystery Novel (Endless rewards, tiers 20-29)
Day 99, 12:00, for 12 hours: 107 zombies at ×21 health and ×24 attack.
Part of Endless tier 20, day 4 of 5.
When it ends: All-Purpose StrengthenerFine Sheet MetalScrap MetalCold CutsMystery Novel (Endless rewards, tiers 20-29)