Robert Silverberg

“ Harrell drove the alien back ... back....
And the Dimellian was eleven feet high.
"We can keep this up forever," Harrell said. "Getting larger and larger. This is only a mental conflict." He shot up until he again towered a foot above the alien's head. He swung downward two-handedly with the machete....
The alien vanished.
And reappeared five feet to the right, "Enough of this foolishness, Earthman. Physical conflict will be endless stalemate, since we're only mental projections. You're beaten; there's no possible way you can defeat me, or I defeat you. ”

“ Harrell-three and Harrell-four, you're to attack physically, one armed with sword and one with blaster, from opposite sides at once. That ought to keep him busy, while he's fighting off the rest of you. ”

“ They would attack the Dimellian simultaneously. Or, at least, five of them would, creating a diversionary action while the sixth—Harrell-original—made a frontal assault on the castle.
Harrell-original faced his five duplicates and briefly instructed each in his job. They were like puppets.
"Harrell-one, you're to attack in conjunction with Harrell-two, on the mental level. Take turns heaving mental bolts at the alien. While one of you is recharging, the other is to unload. That won't give him time to get any sort of defense organized and certainly no counter-attack. ”

“ A fight in which both participants could change size at will, vanish, reappear, and do other such things was as pointless as a game of poker with every card wild.
But there had to be a way. Mental attack? ”