In the Stan's Soapbox in Heroes Reborn: Doomsday #1 (2000), we get a very good question:
Nope...it turn out to be the demon vice of...gambling:
Would telepathy give Charles Xavier a big advantage in Las Vegas?
Not against the house in most games. Roulette? Craps? Keno? Slots? Video Poker? In none of those games does the dealer know what's coming, so telepathy wouldn't be of any real help.
Same for most of the card games: Let It Ride, 3 Card Poker, Caribbean Stud, Pai Gow...in all of those games, the dealer doesn't look at their cards until after all the players have made their choices. Telepathy? Not much use.
Unless...some people believe that the croupier can influence where the ball drops in roulette, and that the shooter can influence how the dice end up in craps. Of course, if this were true, the house would rapidly lose tons of money on those games, and the casinos would running them. But let's assume it's at least possible. Well, if Xavier could control the dealer/croupier/shooter with his mental abilities, he could (theoretically) substantially influence the outcomes, and turn the odds in his favor. Of course, that would be totally cheating, and immoral, but hey, Blackbird fuel don't come cheap.
But what about Blackjack? The dealer doesn't usually doesn't know what his down card is, unless he has a ten or ace face up, in which case he checks for a Blackjack. So, in about 38% of the hands, I suppose Xavier could benefit from reading the dealers' mind. Which is fairly substantial in a game where the house edge is fairly low. But that's no guarantee of a victory...you still are at the mercy of the next cards you or the dealer take, and your mental powers can't influence that.
Of course, Stan does say "incredible mental prowess," so maybe he's not talking telepathy, but smarts. Maybe Xavier's a card-counter!! If done right, that would put the odds slightly in your favor, although it's hardly a guarantee of winning a fortune (no matter what certain Hollywood films might want you to think). To take full advantage, you have to vary your wagers, betting more when the deck is in your favor, less when it's not. And the casinos are pretty good at noticing those patterns, and tossing your butt out.
Unless, of course, Xavier did indeed use his telepathy, to make sure no one noticed his volatile wagering, or forgot about it. Hidden card counting, together with reading the dealers' minds when they do check the hole card, would would turn blackjack from a game with a .5% house edge (assuming perfect play) to one with something like a 2.5-3% edge for the player. You'd still need a huge starting bankroll, and hundreds and hundreds of hours to accumulate a fortune. But it would be doable.
What about playing against other humans, as opposed to the house? Telepathy would of course be a huge advantage in poker. And in sports betting, Xavier could potentially influence the outcome of games, either by mentally nudging players to make mistakes (hello, Bill Buckner--you're off the hook) or telepathically sharing game plans with the other team, and thus clean up on the betting.
But c'mon, Charles...cheating against normal humans just to enlarge your own fortune? Not terribly ethical...Then again, recent Marvel history tells us Xavier enslaves sentient computers and erases memories of dead brothers, and is a right bastard. So maybe influencing sporting events and poker games to enrich himself wouldn't be too much of a stretch...
Or he just sent Longshot...