Back when I briefly dabbled with snakes, I wanted to obtain a carpondro. Never did, though.
On a tangent in a similar vein, I have kept a decently varied collection of chelonian hybrids. Like with their parent species, personality truly came down to the individual animals. I find that when people try to play up or play down personalities to an extreme (especially when dealing with regional variants within a species), there is often a repeated mythology involved or someone somewhere trying to sell something. That said, there are certainly trends here and there.
Many of the following are some I have either owned or spent some degree of time with.
Map x DBTs: I noticed no discernible differences between the hybrids or the parent species in terms of personalities. I *think* skin sensitivity leaned towards the DBT side of things, but I have not had enough to say if this is a rule. Stunningly beautiful hybrids with highly individual appearances that tend to beat the pants off of the parent species.
Map x RES: No discernible differences in terms of personality. Some animals are prettier than average, but I found most I have seen to be somewhat more dull-colored than either parent species.
Crosses between wood, Blanding's, EPT, WPT, and similar turtles: No huge personality differences for the ones I have had the pleasure of meeting, but this is a generally friendly and intelligent group of parent species, too. Adding insculpta or marmorata to the mix seems to boost personality some, but that could be as much my bias as it might be a legitimate observation. The individual appearances are consistent within a cross of this type, but the different crosses differ in parents species influence relative to other crosses.
Terrapene hybrids: Most box turtles are friendly already. Most boxie hybrids and crosses tend to mutually dilute the parent species colorations. I think the ornata x carolina have some interesting appearance potential, depending on the carolina subspecies involved. One should note that there are numerous people who try to use hybrid and intergrade claims to skirt state rules/laws. I see a lot of people labeling EBTxTTBTs and straight EBTSs as WBTxTTBTs. This can be especially obvious as a business move when some people call what seem to be FBTs as WBTxFBTs (although there are certainly crosses of these types out there, too, so we should avoid rushing to judgment).
Many sidenecks can hybridize as can many Cuora. Snappers and Chinese bigheads might be able to if they do not kill each other. Common and alligator snappers can hybridize (I think they are pretty cool and might like one, but now is not the best time for me). Manouria and Gopherus should have a pretty good shot.
The Testudo (and former Testudo) species can pretty much all get it done. All relatively personable like the parent species.
Indotestudo seems to be able to easily cross within the genus.
Radiata x redfoot: A neat-looking hybrid. No idea what their personalities are like, as I have only seen photos.
Radiata x sulcata: Looks like a sulcata with a slightly higher dome and the carapace scutes have some rays to them.
Leopard x sulcata: The overall morphology of these is similar. The main variations are lighter versus darker coloration and medium-large versus large-huge size. The personalities are robust. I think they can be slightly more susceptible to RNS stuff than sulcatas, but less than the pardalis species on average. These are really cool animals to keep in my experiences. Mine do not dig their own burrows, but will use sulcata burrows. Fearless and dominant. High-domed like leopards. Develop thick forelimb tubercles like sulcatas. In the right climate, these are really nice for yard grazing.
Leopard x redfoot: I only have one, but mine is insanely friendly. Stares at my face and will ignore food to look at me (it really focuses on the face). Orange and peach skin with striping. Marbled/variegated shell (even more apparent when viewing the plastron). The shell shape is an even combination of redfoot and leopard morphology. The head is more leopard-like with some redfoot accenting (such as the rings around the irises of the eyes).
RFxYF/YFxRF: I have only had the pleasure of owning one of these (and she is now a classroom pet), but have also known/met several others. These vary significantly. Some are dead ringers for one parent species or the other, so these need good/better records/IDs if they are to be produced or sold off. Personalities are similar. The YF marginal scalloping may be present as a neonate, but is more nuanced and recedes more quickly than in pure denticulata. Could get anywhere from medium to large. I personally prefer the YF-leaning animals in terms of head shape and prefrontal scale arrangement, but combined with a more orange color contribution from the redfoot parent. Because this is somewhat tricky, some better ways to ensure legitimate hybrid status for this cross, as opposed to retained sperm causing monospecific offspring, are to look at the prefrontal scales so that the neonates are the opposite-species configuration of the dam or to isolate the parents consistently and for years (preferably just before sexual maturity for the female if possible, as female YFs can retain sperm for a long, long time).
I am trying, mostly in vain, to produce other types of hybrids and there are many, many possible crosses beyond those I have paid any mention to, but it is slow going. There are prezygotic barriers in the form of disparate size and shape of the parents as well as unwillingness to mate in some (few) cases. In terms of postzygotic barriers, there is a stage where the embryo is just a small clump of cells. The cells either figure things out go-foward complementarity at that point or they do not (and they usually do not). I had to lose a lot of hybrid eggs off various kinds in order to determine what I was observing. To a person not focusing enough, the eggs will appear infertile when they have actually been fertilized effectively. I wonder if employing a forced diapause might make this stage gate somewhat easier or gentler for the cells to overcome, but that will have to wait for later for me.
Dietary and environmental concerns are not big issues at all in my experience thanks to overlapping ranges for parameter optima.
