For a split second, Frank doubted his plan. If he couldn’t use his gift again, if he froze, he was dead. Then he remembered his grandmother’s instructions:
It helps if you know the creature well. Check.
It also helps if you are in a life-and-death situation, such as combat. Double check.
The giant kept coming. Twenty yards. Ten yards.
“Frank?” Hazel called nervously.
Frank stood his ground. “I got this.”
Just before Alcyoneus smashed into him, Frank changed. He’d always felt too big and clumsy. Now he used that feeling. His body swelled to massive size. His skin thickened. His arms changed to stout front legs. His mouth grew tusks and his nose elongated. He became the animal he knew best—the one he’d cared for, fed, bathed, and even given indigestion to at Camp Jupiter.
Alcyoneus slammed into a full-grown ten-ton elephant.
The giant staggered sideways. He screamed in frustration and slammed into Frank again, but Alcyoneus was completely out of his weight division. Frank head-butted him so hard Alcyoneus flew backward and landed spread-eagled on the ice.

The Son of Neptune, Chapter XLVII