noun retÂ·roÂ·gresÂ·sion \Ëre-trÉ-Ëgresh-Én\. : a reversal in development or condition: asa: return to a former and less complex level of development or organizationb: subsidence or decline of symptoms or manifestations of a disease.
Habitat. Slime molds live in somewhat variable habitats all over the world. Generally slime molds live in damp areas of vegetation. They live under rotting logs and damp leaves. Some of the other habitats that slime molds will inhabit include water such as tropical fish tanks.
1 In slime chunks, slimes only spawn on layer 39 and below (feet pos). The spawn rate is equal on those layers.  It's a good idea to hollow out a 16x16 wide (= 1 chunk) and at least 3 blocks high room inside a slime chunk to maximize the spawn rate. Waiting in naturally generated caves and hallways will take much longer.