A new world is recommended for this update but not strictly necessary. There are new structures added and minor world gen changes, but nothing that will cause world corruption.
New Additions:
Many new quest additions
Added Ice and Fire Community Edition
Added Mutant Monsters
Added Monsters in the Closet
Added Mobs of Mythology
Added Mutants and Zombies
Added Rotten Creatures
Added Iron Chests
Added Summoner's Scrolls
Added Serious Player Animations + Serious Reanimated
Added SoundsBeGone
This allows players to disable any sound effect
Added Leaves be Gone
This should help lag in newly generated Spruce biomes
Added ImmediatelyFast (configured to be compatible with ModernUI)
Swapped AmbientSounds for Atmosfera
AmbientSounds doesn't work with SoundsBeGone so this was a necessary change for this new accessibility addition
Added an easy recipe for the tier one recall mirror to make it more accessible early game
Enabled FancyVFX "improved bow" (player and mobs have a circle showing when they are charging their bow and where their projectile will go)
This is configured to be less obstructive than it normally is
Other Changes:
Updated all mods
Enemies now have shorter i-frame window, making them easier to hit with high attack speed or weapons that fire multiple projectiles.
Huge buffs to the Marium's Soulslike Weaponry gun items, making them viable options for a ranged weapon build
Changes to cave generation to make surface caves go much deeper and longer
Changes to the names of some mobs and items to differentiate them from ones with identical names
Armor tweaks to common mobs to assist with early game
Camera sway no longer changes crosshair's position on vertical axis
Fog has been added back to water
Adjusted brightness levels in the Nether
Disabled some dynamic lighting due to performance issues in large structures
Player-held items still work as normal
Jade tooltip now dodges boss/raid bars
Jade tooltip no longer has icons by default (this feature was very buggy and not very useful)
Greatly reduced the amount of time Advancement Plaques will stay on screen
Reduced the number of bubble particles in bubble columns by 95%
This will massively reduce the noise and lag in Bathhouses
Reduced the amount of smoke emitted from campfires
This will help improve lag in villages
Changed default damage particle behavior to "rising" (was "has gravity")
This should improve damage particle visibility when fighting large mobs like bosses
In-world health bars now work properly with shaders enabled
Greatly improved default appearance of Euphoria-patched shaders
Disabled dynamic handheld lighting in default settings of pre-installed shaders (this prevents it from being rendered twice)