Spawns 3 orbiting Cast Gems that can be thrown in the direction Isaac shoots, and will aggressively home in towards enemies.
Upon hitting an enemy, Cast Gems deal damage equal to Isaac's Damage + 2 and stick themselves to the enemy, applying a stack of bruising for 10 seconds.
Bruised enemies take 1 additional damage from all sources for each stack of bruising.
If either the enemy dies while the Cast Gem is embedded; when the duration of the stack of bruise runs out; or if the Cast Gem miss their target and hit a wall, the gem will fall to the ground. Walking over the fallen Cast Gem will pick it back up, allowing it to be thrown again.
Notes
Cast Gems orbiting Isaac will not block projectiles, nor deal contact damage.
Cast Gems have a rate of fire of 3 Gems per second (1 for every 1/3rd of a second) that is not influenced by Isaac's fire rate.
Cast Gems have infinite range and will fly over obstacles when thrown.
The aggressive homing of Cast Gems can sometimes cause them to make circles around an enemy in an attempt to hit them.
Isaac's shot speed will increase the speed of the thrown Cast Gems.
All Cast Gems will return to orbiting Isaac upon entering a new room.
With multiple copies of Nyx, each copy will grant 3 Cast Gems.
Interactions
BFFS!: Familiar modifiers will have no effect on the Cast Gems.
Lost Contact: Cast Gems gain a shield when thrown that will block enemy projectiles and reflect them back, which can deal damage to enemies.
Technology Zero: Thrown Cast Gems will connect with other thrown Cast Gems with a laser, including those embedded inside enemies or those that have fallen to the ground.
Pisces / Knockout Drops / Blister: Cast Gems will create a shockwave on hit, knocking back enemies in its radius.
Neptunus / Pisces: Cast Gems create a splash of water on hit, knocking back enemies in addition to dealing 20% of Isaac's damage to enemies in its radius.
Mars / Toy Piano: Cast Gems embedded inside enemies create a circular aura that applies doom to enemies inside its radius.
Prank Cookie: Cast Gems embedded inside enemies have only an 11% chance to create a doom aura.
Technology / Technology 2 / Jacob's Ladder / Tech.5 / Tech X: Cast Gems embedded in enemies will create chains of lightning between other nearby enemies when they take damage. The chained lasers each deal Isaac's damage.
The number of chained lasers scales with the number of laser items held by Isaac.
Imp Soda / Sodalite Geode: Cast Gems have a 10% chance to deal a critical hit on hitting an enemy, dealing 5× Isaac's damage.
Cast Gem: As the trinket acts as a single standalone gem from Nyx, it will grant Isaac an additional gem for a total of 4 Cast Gems (before Trinket Multipliers).
Nyx is a reference to Hades, a 2020 roguelike dungeon crawler video game.
The costume and effect granted by Nyx is directly based off of the main playable protagonist, Zagreus, and his Cast ability. In addition, many of Nyx's Cast Gem's synergies are based off of the different boons that can be acquired in the game.
Nyx in Greek mythology was the primordial goddess of the night. Nyx is also a character in the game Hades, and supports the main character throughout the game.
BFFS!: Familiar modifiers will have no effect on the Cast Gems.
Scorpio / 
Dead Tooth: Gems will create a poison cloud while embedded to an enemy.
Lost Contact: Cast Gems gain a shield when thrown that will block enemy projectiles and reflect them back, which can deal damage to enemies.
Technology Zero: Thrown Cast Gems will connect with other thrown Cast Gems with a laser, including those embedded inside enemies or those that have fallen to the ground.
Pisces / 
Knockout Drops / 
Blister: Cast Gems will create a shockwave on hit, knocking back enemies in its radius.
Neptunus / 
Mars / 
Toy Piano: Cast Gems embedded inside enemies create a circular aura that applies doom to enemies inside its radius.
Prank Cookie: Cast Gems embedded inside enemies have only an 11% chance to create a doom aura.
Technology / 
Technology 2 / 
Jacob's Ladder / 
Tech.5 / 
Tech X: Cast Gems embedded in enemies will create chains of lightning between other nearby enemies when they take damage. The chained lasers each deal Isaac's damage.
Imp Soda / 
Sodalite Geode: Cast Gems have a 10% chance to deal a critical hit on hitting an enemy, dealing 5× Isaac's damage.
Cast Gem: As the trinket acts as a single standalone gem from Nyx, it will grant Isaac an additional gem for a total of 4 Cast Gems (before 
Trinket Multipliers).
