4 difficulty phases, one every five levels
Data from build 23363152, updated
Every fifth level a new moon rises over the run and changes the rules. The Crescent Moon comes up at level 5, then the Half, Full and Super Moons at 10, 15 and 20, and the Super Moon stays for the rest of the run. Each one lists its own changes: the truck healer restoring less, monsters overcharging your grabber, pits doing less to the monsters you throw into them, and on the Super Moon, enemy orbs that explode when destroyed.
The moon is set by how many levels your crew has cleared, not by time or by quota. Levels 1 to 4 run with no moon at all; the Crescent Moon rises on level 5, a new one every five levels after that, and the Super Moon stays up for the rest of the run once it arrives.