Preheat the oven to 325 degrees F and line a baking sheet with parchment paper. Lightly toast the pecans in a large saucepan over medium heat, about 5 minutes; transfer to a large bowl. Add the cereals and pretzels to the bowl and set aside.
Wipe out the saucepan. Add 3 popcorn kernels and the vegetable oil and heat over medium heat until 1 kernel pops; add the remaining kernels, cover and cook, shaking the pan occasionally, until the popping subsides. Remove from the heat and add to the cereal mixture; toss to combine.
Combine the butter, molasses, corn syrup, heavy cream and a pinch of salt in a medium saucepan and bring to a boil over medium heat, stirring occasionally. Cook, stirring, until the mixture is thick and pulls away from the side of the pan, about 5 minutes. Remove from the heat. Once the mixture stops bubbling, stir in the vanilla. Pour over the cereal-popcorn mixture, season with salt and toss with a rubber spatula to coat.
Spread the snack mix on the prepared baking sheet. Bake until the popcorn is crisp, about 15 minutes (the praline sauce will still be soft). Remove from the oven and use a flat metal spatula to flip the mix in large sections. Let cool completely. (The snack mix will harden as it cools.) Sprinkle with the confectioners' sugar and gently toss to coat. Store in an airtight container for up to 5 days.