An idea i had myself for a knife + haemolacria synergy was a bloodied bundle of kitchen knives being lobbed up into the air and splitting into a spiral of flying knives,,

While the implemented mom's knife + my reflection is nice, I don't think it's too helpful or respectful of the actual item's spirit, just essentially being "you can shoot faster now." An idea I had was that picking it up would cause the knife to move in a narrow loop, sending out slightly left of you, moving towards the peak where the normal knife would go, and the returning in a loop to the right of you. This would make it more like my reflection in which it's more likely to hit more enemies on the way back, while also giving it that slight awkwardness to use that my reflection is known for. Lmk if you like the idea!

Mom's Knife + Continuum
Instead of the knife coming back to Isaac and going crosscreen, the knife continues to wrap around, following Isaac's movement.

i think Mom's Knife with Fire Mind or Bird's Eye should leave a trail of fire where the knife goes

While there is already a synergy with mom's knife and brimstone, make it so that getting second brimstone gives the knife a short range spinning brimstone beam cross from it so that players wouldn't get discouraged from getting the knife after getting the double brimstone synergy.

explosivo: the knife sticks to the enemy dealing continuous dmg then explose once dead or a few seconds passed. you don't get the knife back until it exploses.

C section: fetuses holds a knife, and of course it deals even more dmg. but also increases the hitbox (don't know about c sections synergies, is this one already made in og game ?)

monstro's lung: when it touches an enemy, a barrage of tears is shot from the knife

ludovico technique: the knife now spins increasing the hitbox and control is better also(better than the old one)

tech X: a ring of laser around the knife

technology: some short range laser around the knife shoting repeateadly

spear of destiny: no more familiar, the knife is now a katana, close combat is now deadly. also the knife is longer, so better hitbox i guess

How about Mom's knife and Technology. I know this synergy is exist but i think it needs a rework.

My idea: Knife turns into laser dagger (similar to Spirit Sword), moves faster than original knife but x0,9 damage modifier (unlike Technolohy + Brimstone) because Mom's knife already have damage multiplier

引用自 Raiku：

explosivo: the knife sticks to the enemy dealing continuous dmg then explose once dead or a few seconds passed. you don't get the knife back until it exploses.

C section: fetuses holds a knife, and of course it deals even more dmg. but also increases the hitbox (don't know about c sections synergies, is this one already made in og game ?)

monstro's lung: when it touches an enemy, a barrage of tears is shot from the knife

ludovico technique: the knife now spins increasing the hitbox and control is better also(better than the old one)

tech X: a ring of laser around the knife

technology: some short range laser around the knife shoting repeateadly

spear of destiny: no more familiar, the knife is now a katana, close combat is now deadly. also the knife is longer, so better hitbox i guess

i should mention there is synergies already for c section and monstro's lung, monstros lung simply gives more knives and the c section one is exactly the one you mentioned

just an interaction with dead eye

If you're still adding synergies, maybe one with lachryphagy where the knife has half the range, but at max range it shoots out a bunch of bubbles, similar to brimstone

knife + haemolacria would be so good

Better soy: the knife can go far and back without a charge and can stay out
ALMOND MILK: pure insanity

Mom's knife + brim

Makes the knife red and charged with brimstone and flys noticeably farther and faster and the space between player and the knife has the brimstone beam. The knife still bungees back to the player. Enemies hit by the tip of the knife start bleeding

can you add a synergy that works with haemolacria, brimstone, and moms knife

Maybe soy milk/almond milk makes you continuously shoot out a spray of tiny knives that fall to the ground in front of you, kind of like a short range brimstone+knife?