This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
驑 combines 馬 (horse) with 畱, which likely contributes the sound. The exact historical development is uncertain.
The left side is a horse 馬, and the right side 畱 is a complex shape. Without a clear meaning, picture a mysterious horse with an elaborate saddle.
For リュウ, imagine a rare horse named Ryuu: Ryuu -> リュウ, and this kanji is the only way to write his name.