Master Mode difficulty stacked on whatever mode you pick. Smaller world feel, enemies hit harder, bosses re-skinned, rare drops boosted.

• ▸World feels smaller — visual scale of UI/enemies is enlarged
• ▸All enemies hit roughly twice as hard as Master Mode
• ▸Bosses get new color palettes and behaviors
• ▸Trees explode into TNT Barrels, vampire bunnies replace bunnies on the surface
• ▸Underworld lava is replaced with shimmer
• ▸Many rare-drop chances are doubled

An inverted world — spawn in the Underworld; the world is flipped vertically.

• ▸Player spawns in the Underworld instead of the surface
• ▸Sky and underworld layers swap — Space biome is below dirt layer
• ▸Gravity-related effects feel flipped during exploration

Almost the entire world is Jungle. Constant Queen Bee threat.

• ▸Surface, Underground and Cavern layers are all Jungle biomes
• ▸Almost every chest contains a Beenade
• ▸Queen Bee can be fought repeatedly with cheap larva access
• ▸Honey blocks and hives are far more common than normal terrain

Both Corruption and Crimson generate, plus visual silliness.

• ▸Both Corruption AND Crimson biomes generate in one world
• ▸Living Mahogany Trees and Glowing Mushroom biomes spawn on the surface
• ▸Sandstorm in a Bottle and Lava Charm both findable in Pyramids
• ▸Enemies sometimes drop unusual items
• ▸Surface backgrounds occasionally swap during night

10th-anniversary world — party visuals, item drops, and special enemies.

• ▸Constant party visual effects — confetti, balloons everywhere
• ▸Music-box items drop from many enemies
• ▸Aprils-fools-style item renames in the UI
• ▸Princess NPC available without the all-NPCs-alive prerequisite
• ▸Coin drops include party-themed cosmetics

Crossover seed with Klei's Don't Starve — Eye of Cthulhu becomes Deerclops-themed, vanity drops.

• ▸Stronger eye-shape and color tint applied to the world
• ▸Deerclops drops include Don't Starve crossover vanity
• ▸Eye of Cthulhu visual reskin matches Don't Starve aesthetic

Dungeon traps are replaced — visual recoloring of pressure plates and dart traps.

• ▸Trap-related tiles are recolored / cosmetically replaced
• ▸No mechanical changes to drops or progression

The ultimate challenge seed: every other secret seed's effects combined.

• ▸Combines 'for the worthy', 'don't dig up', 'not the bees', drunk world and 'don't starve' simultaneously
• ▸Most difficult seed in the game — recommended only for veterans
• ▸All boss palette swaps active
• ▸Both evils + jungle-everywhere + flipped world + party effects