Standing the dessert alone with prickly needles I adore

I dance upon the waves at night, a silver path of borrowed light. I touch the ground yet leave no trace, a quiet glow in every place.

What do you call a bear with absolutely no teeth?

I am a mixture of different genetics, from a small mutation that makes two different color patterns, to a mythological beast with parts of several different species.

A guardian of some renown, I perch like a spear. I sit beneath the crown, and strike any who draw near. I am a brethren with a spine, and may let you enter my hall. Against giants I hold the line, but not those who are small.