Lifeblood

Lifeblood is an update to Hollow Knight whose open beta was released on March 23, 2018. As it was not one of the three originally planned DLC updates, it did not release with a teaser. It was mainly technical, and focused on bringing upgrades and optimizations of various kinds into the game.

Bosses

 * Hive Knight

Mapping Tools

 * Map Markers

Main menu

 * Players became able to change the background of the title screen (Extras section)
 * The menu styles include:
 * 1) Classic (Unlocked from start)
 * 2) Hidden Dreams (Hidden Dreams update)
 * 3) Grimm Troupe (The Grimm Troupe update)
 * 4) Lifeblood (Lifeblood update)
 * 5) Infected (Unlocked by beating The Hollow Knight)
 * 6) Void (Unlocked by beating The Radiance)
 * 7) Steel Soul (Unlocked by completing Steel Soul Mode, any ending)
 * A changelog was added, which includes information about every major version of the game (Extras section)
 * Blur quality can be changed through the Video menu

Visual Changes

 * The Hive area gained a complete visual redesign
 * Improved color pallet for many areas
 * The Zote Statue implemented in the Hidden Dreams update now only has four candles
 * Lighting is more bright and livid, with a more blueish hue
 * Dirtmouth's Stagway now has a billboard
 * Small foreground spiders may appear and scuttle away from the player's feet when exploring Deepnest
 * Animation for traveling the stagway has been tweaked with hanging lights, and is now able to be skipped
 * Mid ground and background perspective movement is a lot smoother and clearer
 * Using Crystal Heart Dash now gives off a flash of purple light (the animation may also be quicker)
 * Tram pass slots now have a glowing yellow light
 * Calling and riding the tram now has a rippling effect overlay
 * Sections of Ancient Basin and Kingdom's Edge are noticeably more blue toned
 * Shadows for many objects, unkillable organisms (spike worms on the floor) and environments have sharper and more contrasting shadows
 * New transitions have been implemented and the scale and zoom of the camera may have been tweaked (?)
 * The lights of the houses in Dirtmouth are more vivid and noticeable
 * Forgotten Crossroads loses saturation and is more gray scale once it turns into the Infected Crossroads
 * The Hollow Knight (player) now has a new burst animation when taking damage
 * More decorative lanterns have been placed around the place
 * Entrance to the False Knight boss fight now has a furnished gateway
 * The lighting fading and transitioning from area to area has been modified
 * Decorative mushrooms in the foreground of Fungal Wastes now react to the player walking over them and let out a puff of spores
 * Smacking and breaking many decorative pieces will now cause a ripple effect overlay (?)
 * The greenhouse where the two Shrumal Ogres are fought is now a vibrant green
 * The arena for the Lost Kin loses saturation and is more gray scale

enemy Changes

 * Hivelings are now much larger and have more Hp
 * Traitor Lord gained two new attacks and now deals two masks of damage and is a lot faster
 * The Hollow Knight's diving flame pillar attack now does two masks of damage
 * The Collector can now be staggered
 * Nightmare King Grimm can now only be accessed while wearing the Grimmchild charm
 * Soul Master's size has been decreased considerably
 * Many enemies and bosses have had tweaks to their colours making them more vibrant against the environment (?)
 * Soul Tyrant can no longer be staggered
 * Hive Guardians do two masks of damage
 * Volatile Mosskin Explode faster upon death
 * Desolate Diving onto Flukemarm no longer functions
 * Husk Hive is larger and can spawn Hivelings on the move instead of stopping (and faster?)
 * The Hive now contains a higher amount of enemies (?)
 * Aspid Hunters are now a more brighter orange to match the rest of the infected enemies
 * False Knight's stagger animation is faster
 * Fungified Husk's spore cloud is significantly bigger
 * Traitor Lord has a visual cloud of infection surrounding him

NPC Changes

 * The Dung Defender now has extra dialogue after the player beats the White Defender multiple times
 * Divine now has extra Dialogue when the player talks to her while wearing the Defender's Crest
 * If the player encounters the new dialogue from the Dung defender, leaves his home and returns there is now a seventh dung statue in addition to the five knights and the king; one of the player hollow knight
 * Dreamer sequence after first Hornet fight has new animations
 * New Dialogue from Hive Queen Vespa once the Hive Knight has been defeated

Charm Changes

 * Flukenest's damage has been nerfed and now costs 3 notches
 * Weaverlings do more damage with a new attack animation
 * Flukenest now has a blue dot when it is hovered over may be just a visual glitch (?)
 * Weaversong and Sprintmaster have a new interaction which causes the weaverlings to move faster and wander a bit farther from the player
 * Weaversong and Grubsong now have a new interaction which causes damaged weaverlings to give the player soul

Audio Changes
(note: taken from the /r/HollowKnight subreddit, editing is needed credit due here: https://www.reddit.com/r/HollowKnight/comments/86tqh5/spoilers_compilation_of_changes_with_lifeblood/)
 * Fungoons has a new attack sound.
 * Bluggsacs has a new disgusting sound when you're nearby.
 * Fool Eater has a new attack sound.
 * Mosscreeps has a new sound and you should feel ashamed if you hurt them.
 * Siblings has a new sound when they spawn:
 * Crystallized Husks has a new attack sound:
 * Wingmould has a new sound when you hit them:
 * Shrumal Warrior has a new death sound.
 * Shrumal Ogre has a new death sound.
 * Shrumelings has a new adorable sound for when they pop up and run away
 * Volatile Mosskin has new attack and death sound.
 * Mosskin has a new attack and death sound.
 * Moss Knights has new attack and death sound.
 * Gulkas has a new death sound.
 * Mistakes has a new death sound.
 * Sporgs has a new sound when they pop out to attack
 * Glimbacks has a new and louder scuttling sound whilst patrolling
 * New audio for locked arena/waved-styled fights
 * New sound for when you place a Dream gate in an invalid location
 * Dreamshield makes a 'tink' noise when it passes over a piece of geo
 * Dung Defender and White Defender now audibly pounds his chest when he transitions
 * Mantis Lords sound for when spike pops up in the beginning has been changed.
 * New OST for arena/wave-styled fights in City of Tears
 * New sound for breaking mushroom flora in Fungal Wastes.
 * New sound for breakable pipes and such in Royal Waterways.
 * Bretta is now audibly scared when you first find her.

Misc. Changes

 * Inventory dropping (speedrun strategy) has now been removed
 * Controls for The Knight seems to have been 'tightened' and the knight also seems to fall faster (need confirmation)