Line a large baking sheet with parchment paper or wax paper. Ensure you have enough counter space for it to lay flat.

In a very large mixing bowl, combine the Chex cereal, small pretzels, and optional nuts. Gently toss them together for even distribution.

Place the white chocolate chips or wafers in a microwave-safe bowl. Heat in 30-second intervals, stirring well after each, until smooth. Alternatively, use a double boiler on the stovetop: place chocolate in the top bowl over simmering water and stir constantly until silky smooth. Avoid overheating.

Pour the melted white chocolate over the dry ingredients in the bowl. Use a rubber spatula to gently fold and coat everything evenly. Scrape the bottom to incorporate all chocolate.

Pour the coated mixture onto the prepared baking sheet and spread into a single, even layer. Immediately sprinkle the green and yellow M&M's, Lucky Charms marshmallows, and St. Patrick's Day sprinkles over the top. Gently press them into the chocolate to help them stick.

If using, melt the green candy melts as you did the white chocolate. Drizzle over the top of the leprechaun bait.

Let the Leprechaun Bait sit at room temperature for 1 to 2 hours, or refrigerate for 15 to 20 minutes, until the chocolate is firm.

Break into snack-sized pieces. Serve in a bowl, individual bags, or as a topping for ice cream.