Clidastes, as the smallest mosasaur, is unique in that way at least. Its small size allowed it to be a quick and agile swimmer that was capable of chasing down some quick and diverse types of prey. In this Dan Varner illustration a Clidastes is chasing down a turtle, which may or may not be a preferred food item. Considering the smaller teeth of Clidastes I would think that a turtle would not be a main dietary choice for these animals, however, this depiction could be of a young mosasaur as well. Young mosasaurs, if they were independent hunters, under a mother's supervision and encouraged to indulge their interests and learn for themselves (or they were orphaned) may have attempted to eat prey that they would not normally have attempted to delve into. Also, for the future discussions, in about ten seconds, note the caudal limbs and the thick paddle of the tail.
The tail and caudal limbs are of important note in all illustrations of Clidastes are important to pay attention to. At times the tail appears somewhat fish-like, like an Ichthyosaurus tail, and sometimes, as in all the illustrations I picked today, the oar shaped tail is dominant. There is a difference of opinion amongst experts and most seem to prefer the oar shaped tail, though, considering that there would likely be no bones in a large fish-like tail, the possibility of a strong swimmer such as Clidastes adapting to its environment by developing a large fish tail rather than an oar like tail like its bigger cousins and sisters is not very far fetched. However, the oar shaped tail could be just as powerful as a deep fish tail if it too was deep and had sufficient muscle attachment to power it. The caudal limbs I also suggest noting due to the fact that the caudal limbs are never illustrated in the exact same manner. In this illustration the limbs are rather hand like, at times they are paddle like and other times they seem to be not much larger than the pelvic fins of sharks.
The mid-sized caudal limbs of many illustrations are fairly typically ovals attached to the body. The oar shaped tail here is nice and deep, conveying that sense of power a bit more than a shallower oar. The head, I think, is a bit more Tylosaurus like than it is Clidastes like, however, considering we do not have a "mummified" Clidastes skull to compare the skin impressions to the fleshed out drawings and illustrations of modern artists. The agility of Clidastes, somewhat rarely overall, is shown here as it is chasing down some small and fast prey items. Overall, most Clidastes images look very similar, and consensus in the art community is not a bad thing, but there is enough variation between artists and images exists that looking at these images in contrast to one another can be an all day activity.