Bruce erected a new, spiraling pillar immediately to Prisma's left, culminating in a chute that Bruce dropped down into, deconstructing the platform he'd been standing on and layering the outside of the pillar with that material, adding in various types of rock, dirt and sand into the mix, expanding it more and more as a type of shield between his body and Prisma's hand that was gathering energy. The chute had numerous paths to the outside observer, but the inside only led as far the side of the giant opposite his lowered hand as possible. As he moved, Bruce made use of some of the excessive ki, the leak of which he'd managed to learn to stem at least marginally, to reinforce what acted as a shield between him and the oncoming blast. 
As a means of being proactive, he also made one of the outer paths of the chute wrap around one of Prisma's legs- ideally it would aid in, if not restricting, at least slowing the giant down if he got it into his head to move somewhere.