The Gravity Gem is a very tricky gem to battle, especially with projectiles because they are sent everywhere. It's not dangerous unless those projectiles fly back at you. Ceaira and the others faced Gravity in Episode 6. It takes on the form of a young teenage elf with a mystical amulet around it's neck. This amulet controls the gravity powers.
When Ceaira fought it, she had to knock it out before sealing it. She did so by focusing all of her magical powers into one large blast of ice shards. After the gravity effects wore off, she followed up with Amazon to trap him, allowing his capture. When summoned, the amulet causes a change in gravity to make the atmosphere lighter or heavier. Ceaira will have used each effect at least once before the end of season 1.