I’m a big fan of multilateral combat encounters, and the egg hunters in Fizban’s Treasury of Dragons are a sly way to throw in an extra dimension of conflict: parasites that feed on dragon embryos and lay their own eggs in the emptied shells.
To a dragon defending a clutch of eggs—like the black dragon Mundirostrix in Live to Tell the Tale—a party of bloodthirsty adventurers may pose a clear and present danger, but all that will be forgotten in an instant if the dragon spies an egg hunter skulking around. The horror and revulsion, fear and fury that these minuscule monstrosities evoke in dragons overwhelms all other considerations. First, the dragon will try to whisk its eggs out of the egg hunter’s reach; second, it will turn all its attention and efforts toward obliterating the parasite.
This distraction may allow a party of player characters to punch above their weight, taking on a dragon that would normally be too much for them to handle. Don’t assume, however, that just because the PCs are enemies of the dragon, an egg hunter—or its hatchlings—are friendly to them.