Valkour’s fiendish fire

When all seems lost on the battlefield, a small drop of your blood into a small vial of alchemist’s fire can make a large difference. Upon performing the spell, you splash a vial of fire tainted with blood at your feet, summoning an unusually bright ring of flames with a circumference of 20 feet. Any approaching enemies  are instantly driven back, and cannot pass through the fire without taking 1d10+4 burning damage per round. During the duration of the spell, you are unable to move, and can chose to alter the shape of the flame to part for allies or thicken for foes. You may chose up to ten people to be resistant to the flames, so they may not take any damage while you are casting, but you may only do so for three rounds and only as long as you are very concentrated.