Air Bubble (homebrew)

You create a bubble of air around the head or the body of one willing medium sized creature you can see within range. The bubble is filled with fresh air that lasts until you end concentration. At Trained level, you can create a bubble large enough to hold 4 medium sized willing creatures or 2 large creatures or 1 huge creature. At Mastered level, you can create a bubble large enough to hold 8 medium creatures or 4 large creatures or 2 huge creatures.