TerraFirmaCraft implements a new mob spawning system where hostile mobs only spawn below Y 128 (can be disabled in the config). Hostile surface animals such as bears and other predators still exist as an active threat on the surface.
Mobs are unaffected by light levels during spawning. Due to hostile mobs only spawning below Y 128, no hostile mobs will naturally spawn at night time on the surface aside from preexisting predators.
New wild animals such as cows and sheep will occasionally spawn, often in packs.
TerraFirmaCraft has a protection system where spending a fair amount of time in an area renders the area "protected" - preventing hostile mobs from spawning in said area. There can be multiple protected areas and the protected areas will gradually decrease the range of protection if the player is no longer spending time in the area.
The range of this protection area is a 5x5 chunk area centered on the chunk the player is spending time in. In multiplayer, players close to each other in the same area can double the speed of this protected area coming into play due to each individual player contributing individually to an area becoming protected.
It takes 6 in game hours to accumulate full protection - 24,000 ticks at 500 ticks / 5 seconds (or 100 ticks / s) = 240 s = 6 in game hours. After reaching full protection at 24,000, the game will continue to allot protection as there is no cap.
Spawn protection does not stop hostile mobs from spawning below y-level 100 by default.