The Aqua Brace is a flying enemy found in Kerguelen Plateau. It attacks by launching itself at the player and rebounding off terrain in a chaotic manner.
After spotting the player, the Aqua Brace starts spinning rapidly in place and then launches itself at the player at high speed. It will rebound off any solid terrain it touches while spinning, making it dangerous alone and extremely dangerous in groups. The rebounding seems random, but the Aqua Brace is actually tracking where the player is to a degree, making it necessary to move constantly to avoid being hit.
Attacking Aqua Braces using a weapon with sufficient knockback will send them spinning in the opposite direction. Remain calm and patiently bat them away until they stop spinning, then close in to finish them off. Be warned that certain attacks with low knockback, like the shots from the Gunslinger's 
Kinetic Revolver as well as Spin Kicks, will not cause the Aqua Brace to rebound.
There are two tougher versions of the Aqua Brace called the Silver Shield and the Oceanic Bastion.