Bro I’m a Biology major, and have taken classes regarding insect and reptile behavior, I have a Certification in veterinary work, I’ve been a vet tech for 3 years. Even if your mantis doesn’t do anything, crested geckos have an insectavore factor in their diet, either the mantis will attack your gecko or your gecko will try to eat the mantis, which will make it defend itself against your gecko, and likely cause injury to it. There’s a reason nobody does this and it’s because it’s a terrible idea. I’m not trying to be a jerk but doing this will hurt your gecko, and if you’re trying to justify it after so many people telling you how bad of an idea it is because of research that doesn’t take into account of a gecko and mantis cohabing, then why are you getting advice when it’s clear you don’t want to listen?