User blog comment:Dragonmentor123/Is there a reason that Toothless might be the only night Fury?/@comment-25145866-20140823185729

Here's what I think:

Toothless, when younger, might have gotten seperated from the other Night Furies when they were leaving their old habitat in the Barbaric Archipelago. Reason why they left might be because their habitat got destroyed by, lets just say, a volcanic eruption. After that, he might have joined the other dragons and  lived in the Dragon's Nest until he was shot down by Hiccup and live in Berk.

Yeah, that's what I think happened. He might reunite with other Night Furies in the future, maybe in the new upcoming series or HTTYD 3.