Preheat your oven to 350°F (175°C). This ensures that your brownies bake evenly.
Line your 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal later. Lightly grease the paper with a bit of vegetable oil.
In a large mixing bowl, whisk together the vegetable oil, granulated sugar, unsweetened cocoa powder, eggs, vanilla extract, and water until smooth. Add the salt and all-purpose flour, mixing just until combined. Be careful not to overmix!
Pour the brownie batter into the prepared baking pan. Bake in the preheated oven for about 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Let them cool slightly in the pan.
While the brownies are baking, melt the unwrapped caramels with 3 tablespoons of milk in a microwave-safe bowl. Heat in 30-second intervals, stirring between each, until smooth and creamy.
Once the brownies have cooled for about 10 minutes, spread the marshmallow fluff evenly over the top. Drizzle the melted caramel over the marshmallow fluff, creating a marbled effect.
In a separate bowl, melt 2 cups of chocolate chips with 1 tablespoon of vegetable oil in the microwave. Stir until smooth, then pour over the caramel layer. Sprinkle chopped peanuts on top and finish with the remaining chocolate chips.
Return the brownies to the oven for another 10-15 minutes, until the top is set and the chocolate is melted. Allow the brownies to cool completely in the pan before lifting them out using the parchment paper.
Once cool, slice the brownies into squares and serve. Enjoy the gooey, decadent layers of your Snickers Brownies (ChocoSmash Bar Copycat)!