Charles Ellicott Commentary Daniel 8:24

"And his power shall be mighty, but not by his own power; and he shall destroy wonderfully, and shall prosper and do [his pleasure]; and he shall destroy the mighty ones and the holy people." — Daniel 8:24 (ASV)

Not by his own power. — Not might, but cunning, will cause his success. (Compare to 1M Malachi 1:10 and following.) Thus his destructive powers become astonishing.

The mighty. — No special individuals are pointed out, but rulers in general.