You could not do it without a securities license and no one would "play" your game when there is a traded "options market" traded on exchanges around the world. In addition it would also be considered gambling, and the fact that you use credits or chips or matchsticks while the game is being played changes nothing.
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
Absolutely not legal -- this violates many of the CFTC rules on futures contracts.
The foregoing is not legal advice nor is it in any manner whatsoever meant to create or impute an attorney/client relationship.