I've had to turn on frame skip to reduce the lag myself.
Anyway, things I've found:
Graveyard biome, just place a load of graves in the same place. Ghosts, ravens and maggoty zombies spawn here, the world goes more monochrome, and fog covers the ground.
Breaking graves seems to have a chance to spawn a ghost offscreen.
Fairies sometimes appear from offscreen. I've only encountered one in a cave and it brought me to a large gold seam when I followed it before vanishing.
Gem trees drop gems and gemcorns. You can also make gemcorns from an acorn and a gem, with the gemcorn's colour being dictated by the gem.
Hitting trees with an axe sometimes makes them drop stuff. Depends on the type of tree, I found that regular trees drop acorns, wood, birds, squirrels, owls (at night), peaches, apricots and apples. Boreal trees sometimes drop cherries. Mushroom trees drop glowing mushrooms and mushroom grass seeds. Not sure about the others.
Trapped chests are now a thing. I saw the explosives, I saw the two dart traps, I figured that the gold chest spawned and broke the pressure plate in doing so. Nope.
In master mode you drop ALL held money. Also mobs holding money are far less likely to despawn so it's easier to get your gold back when you die.
Gold chests can spawn underground outside of shelters now.
Deserts can have oases in them
LILY PADS AND REEDS OH MY GOD PONDS LOOK B E A U T I F U L
Gnomes. Hostile mobs that sometimes spawn. I've killed one so no idea if they drop anything other than gold.
Underground glowing mushroom biomes are way bigger now. They also have a host of their own mobs, like spore bats and mushroom skeletons.Zombies jump to hit you. Not just when they go up or down a block, or there's something in the way. If you try to jump over them they now intercept you mid-air.
Also, is anyone planning on running a server at some point? I'll even help pay towards costs if necessary, but I couldn't run one since I lack both the know-how and commitment to do that aspect of it.