There's no greater joy like a Rider who Merges so well with their dragons they become the Dragon itself.
Such Riders are no longer just Riders—they are also the Dragon. With one mind, one direction, one heart, no command is needed. But it's true that for inferior d bonds, Mergimg is an art that might lead to madness and diminish the life span of a rider, as such, careful practice is required of those lucky enough to possess the ability of the Art.
—Riders and their Abilities by Elara Stormward.
The pit of Vinn's stomach dropped at the revelation from Xander. It wasn't so much as the fact they would possibly be battling six dragons in total that scared her, it was their own strength that she could insufficient.
Carex and Maserti, while impressive on one hand had no special abilities. And even if they did possess one, it yet to be honed.