Hello, this option already exists! Just don't choose a race, visual, and region, and the Mine will give you a totally random creature !
Simply leave the 3 tabs blank, and validate your invocation ! This will remove your 30 crystals and give you a random creature !
Likewise, you can choose a specific race without choosing its visual ( in this case, if you choose for example a Minoushas without choosing its visual, you will have a one in 4 chance of having any of the 4 visuals ) and I believe reversal is possible as well, but I'm not sure about this one.
I do it almost all the time personally, and it sometimes turns out pretty ^^
P.S. Hope this is understandable enough for you, I wrote with google translate ^^"
Have a good day ♥