i know many have asked for more synergies, and i can understand how its hard to make them up, so heres a helping hand.
brimstone+tech 1=brim laser made from tech beams, no diff
soy milk+brim=constant laser, weaker
knife+tech1= electronic knife
knife+teath=random chance upon room spawn for bone knife, badass
death touch+knife=you know
ludo+ipecac=super damaging bomb, once explodes another apears, maybe
brim+teeth=tooth fire rapidly at random, suggested at blood laser in backround
epic fetus+brim=laser from above, takes time to charge, destroys skull things.
epic fetus+knife=same as above
both fetus's+teeth=tooth bombs (:
teeth+tech 1=annoying painful noise+white solid laser
norm fetus= buffed
epic fetus=takes longer to bomb, tear ups decrease time, soy milk means control when explosion happens
norm fetus+brim=bomber man bombs
norm fetus+knife=lokis horns moms knife on spot
moms eye=CONSISTENTLY WORKS, it sucks **** without lokis horns, BUFF IT.
also, more champions. maybe with items such as lokis horns.
champion versions for isaac and blue baby as over characters such as, lazarus, x2 health, half heart damage, once killed play death animation, becomes judas, super low health, high firerate, full heart damage.
once you kill isaac or satan, theres two chests, one bad one good, for more floors, that'd be cool.
new final boss that uses harder versions of your items against you, so it can get daddy long legs, meat boy/bandage girl etc, making it not be a battle of how OP your items are, but a battle of how good you are as a player.
new item that-allows you to hit zombies on all sides, means that enemy's that once dead become other enemies, don't, allows you to kill the living skulls, stops enemies regening, allows you to follow grounded enemies and shoot them (they get a trail that doesn't hurt you) etc.