My idea for a creature within my fantasy story is that of a creature which floats through the air like a living hot air balloon.
It would do this through the intake, storage and regulation of gases within its body alongside its body temperature.
Its appearance is that of a large blob varying in size from a backpack to a small car with a head in front. There would be several long appendages hanging below it to act as limbs, grabbing food to bring up to its head to eat. There are wings but they function more like a parachute to keep it in the air and for balance and directing its body. Its main body would consist of all your standard organs alongside several large sacs for storing gasses and an advanced respiratory system to manage its own breathing and the regulation of its gases.
It is an opportunistic omnivore with its main diet consisting of vegetation and carrion it finds. It doesn't hunt since it's not that hard for anything to get away from it(through running or hiding under cover).
It doesn't need to worry about predators as there is nothing capable of catching it in the air except birds of which there are no varieties capable of taking it down at full size, and even if they hunted the backpack size ones, they taste terrible.
I am undecided on which gas/es it will use to do this, any suggestions are welcome, whatever it is, it will have to be sourced through breathing from a standard earth atmosphere and/or producing it from food sources within its body. The gases will need to be able to produce enough lift for it to float in the air just above treetop level or higher. It can use its own body temperature to increase the lift provided by these gases but that is limited by how high its body temperature can get.
My question is how viable is this creature? could it actually float and survive in an earth-like world?