Gerard braced himself as he watched his cloned lover charging at him at high speed, taking notice of the haki coating her arm. He would have expected that of course. Without haki she wouldn't be able to hit him, and this would have made the entire exercise pointless. But as she closed in, Gerard's body took on its gaseous form and as the fist flew, Gerard dropped.
Though his intangibility was useless against haki, it wasn't without its use in its fight. In his gaseous form, Gerard's body was more fluid, capable of moving in ways a regular couldn't. It was with this flexibility that Gerard avoided Valentine's punch, her fist not connecting with a single wisp of gas.
As he ducked down, he tried to loop his cane around her leg, intent on tripping her up. Timed, unwittingly, with her attempt to blast herself backwards, would most likely trip the kuja clone up, but the sudden momentum would yank Gerard in the same direction, sending Gerard sliding along the sand to where she would end up. Not exactly what the gas man had planned.