Creampie = turn on. Impreg/egg-laying = no f*cking way. Yeah, I know it's all very counterintuitive as far as biology goes.
Femdom over strong, bound monster boys is pretty hot, but definitely not into inflicting pain - unless it's post-orgasmic pleasure, if that counts. Milking machines are awesome. Must stress that taking turns being the dominant, attentive partner is not just interesting, but paramount imo.
Also, I prefer more substance than slime, although
>>5570985 's comment about a slime boy monster turning into living clothes/biosuit is super intriguing. And as
>>5572535 puts it, he's gotta be sentient for that to be particularly erotic.
General favorite fantasy gravitates towards tentacles belonging to the incubus/alien nature, although I also prefer a fantasy monster boy that possesses humanoid arms, torso, and lower face.
As you can see via the progression of this thread, it's very hard to generalize what women like in their monster boy fantasies. And we're only a small fraction out there. Tastes/distastes will always overlap/polarize, and usually has very little to do with gender bias.
Kudos to
>>5570337 , the starter of this discussion, and good luck on your work. It's refreshing to hear you're challenging yourself by listening to input from a different perspective than your own.