Untamed Wilderness (Biome improvements)

Things to make the wild feel more wild.

Dangerous mobs such as packs of wolves that hunt you, as opposed to their lone wolf counterparts. Cougars, which stalk you from the treetops and wait for the right moment to strike. Bears who guard caves filled with valuable ores. Desert snakes that hide in shrubs and attack if you get too close. Alligators who hide underwater in swamps, waiting to maul and drown you. Geese, whose sole purpose in life is to terrorize you.

Additional ambiance such as chirping birds in the forests, buzzing mosquitos in swamps, twigs breaking as you walk (or perhaps that's a cougar), fireflies, fog, and crickets.

Along with a few misc things like dirt eventually turning into mud when adjacent to water, this would slow entities but would improve fertility and wouldn't need to be tilled. Perhaps a temperature mechanic (though this may be possibly more suited to hard and hardcore difficulty worlds) along with seasons (since the world is infinite the effects of different seasons should be based not on latitude but instead biome type, thus preventing it from snowing in the desert). Wild plants that are normally found in villages (such as carrots) in case village generation is disabled. Along with the addition of more things to hunt, like herds of shy deer in the forests and tanky bison in the plains.