Small, vynil-like, helium filled dragons that are weighed down by having a belly-full of water and weight of their solid talons and tail scales. They spit out water to reduce their ballast to float and can expel helium from their nostils if they need to lower. If they end up spitting out all their water they can release just enough helium to just about keep their shape, but be brought down by the weight of their talons/scales.

These creatures always, but very, very slowly generate helium, so all they need if deflated to do is find a safe place, weight themselves down and wait for themselves to re-inflate. They can only exlpel their helium of their own accord, ie, they don't breathe it naturally, so before they sleep they need to fill their bellies with water then deflate themselves to a minimum to avoid floating away or over-inflating while they snooze.