1- you take a bunch of disgusting and horrible things and you put them all together. like, put a cockroach and a spider together and then make the spider as big as a van and give it 3 rows of razor sharp teeth and make this thing’s limbs as long as an average tree then it’s skin should be this disgusting grey color. its breath should be so disgusting that it makes you feel light-headed when you smell it. then you just put some wings on it and there you have it
2- start with a basic shape that you want it to be, then give it way too many sharp teeth and spikes, and then give it a bunch of eyes on various parts of its body, like, on its shoulders or something. finally, give it one really weird trait for no real reason just to spice things up and make it a little extra disturbing
3- you just think really hard about the most ridiculous things you can imagine. like i’m thinking of one right now. it’s black and it lives in a swamp and has a big round body and has one huge leg and it’s face opens up into some kind of gaping maw and then it walks around using its one huge leg to support its massive body while it searches for any unsuspecting passerby and it eats them whole with its giant mouth
4- start with something familiar that scares you, and then distort it and twist it and make it unnatural and unsettling. add multiple eyes or mouths. make it something that makes people want to look away but also makes them want to keep looking at it
5- reference real world animal anatomies and give your monsters a sort of biological plausibility