The problem with getting a certain hybrid is that there are way too many...
My suggestion is to be patient. Look on the kiosk for the EXACT pet you want and look through the stats on which you want your pet, whether it's a ward pet, a damage pet etc.
A lot of the time I fail to but I just keep on trying and I eventually do get what I need. Unfortunately no one really knows the exact chance of getting the pet you want, so I guess it's all on luck.
For the basilisk and Creeper your gonna need to have a hydra first on the sigil or just hatch with one that's already in the kiosk. As for the poised medusa its mainly just luck