Just a short one, which came to me when I noticed a weirdly specific parallel between two of D&D's most prominent non-true dragons. Pseudodragons and wyverns both have poisonous stings, albeit with different types of venom. Wyverns are also bigger, dumber, more aggressive, and have fewer limbs.

My first thought was that wyverns could be war-creatures created from pseudodragons and, I dunno, maybe snakes. (Fewer limbs, deadly poison, it works, right?) That, in turn, lead to me wondering what other reptilian monsters the yuan-ti might try to turn into bestial war-machines.
Maybe medusae could be turned into scaly apes with a mass of snakes coming out of the neck, presumably still with the signature petrifying gaze. Maybe a salamander monster could have a bite that injected liquid fire into its victims. Maybe a grick's tentacles could be replaced with snakes, possibly with suckers on the bottom for extra unnaturalness. Maybe a ravid's positive energy aura could be corrupted into a toxic aura.
Hydras, kobolds, and shocker lizards don't have a lot of room for creativity (big poisonous brute, basic cannon fodder with venom, literal shock troops), but they're still worth mentioning. So is a potential end-goal for a campaign focused on this idea. After all, what (non-draconic) reptilian creature can hope to match the sheer terror induced by the tarrasque? If the yuan-ti can induce a serpentine upgrade, they would be able to psionically control this infamous destroyer of nations and use it to take over the world or whatever! It's a low-hanging fruit of a climax, but sometimes the low-hanging fruit is worth plucking.