Good Ending is a wonderful Vanilla Style mod that adds a whole lot of tweaks to vanilla biomes, a few new props that will appear on your world(such as boulders of all stone types), and blocks to come with that.
It also brings a few new mobs to the table, such as Woodpeckers, swarms of Fireflies and the Marsh swamp monster. Fireflies can be used to make lanterns or transported with bottles to be placed wherever you want, and the Marsh is actually a scared-y little creature that allows you to coat your weaponry in potion effects.
Besides the new mobs, this mod also adds multiple new forms of existing trees that grow when you plant their saplings on specific blocks, like the comforting yet somewhat exotic Muddy Oak Tree and its planks, stairs, etc. Speaking of wood sets, Good Ending also adds Cypress Trees, which have orange planks and a white bark.
Lilypads have been changed to not break when you row your boat through them, and multiple new forms of them have also been added, having flowers of different colors. Cattails and all sorts of colored flower patches will also appear in your world.