Monopoly, but you can also gamble on the yahtzee stock market.

If you're into Chess and Poker there's Choker, aka Texas Choke 'em. Other than that I know about mixing four or nine versions of the Labyrinth game and similar things, but off the top of my head no other mashups come to mind. But it's an interesting idea!

You can get a copy of Reign the Final Battle Royal for like $5, might give you some more components to have fun with

You could also look at Fluxx for inspo, its a game were players add rules as you go. You could do something similar ie new rule you can use monopoly money to buy risk countries.