Grand serpents o dragons, are spirits that represent the calmness and harshness of nature, with the cunningness beyond any animal. They are representative of the sheer elemental powers found in the otherworld.
Whether it's a world serpent of sorts, a dragon deity, or a strong spirit/wight, they all are insanely powerful forces to be reckoned with.
For example, one of the spirits I revere in my practices (via UPG) is the blood serpent, which is an entity that represents the lifeblood of the earth and the leylines. This being could be called a dragon of sorts, and is practically a deity. As a force of nature.
To a smaller extent, I've encountered a winged dragon in the otherworld, and it was still an immense being. Old and dangerous, and quite slow to action.