Heat oven to 250°F. Line a large rimmed sheet pan with parchment and lightly grease.
Combine cereal, pecans, and pretzels in a very large bowl.
Melt butter with brown sugar, corn syrup, and salt in a saucepan over medium heat, stirring until smooth. Bring to a gentle bubble and simmer 3 minutes.
Remove from heat. Whisk in vanilla, baking soda, cinnamon, and cayenne. The syrup will foam slightly.
Pour the foamy praline syrup over the cereal mixture. Toss until everything looks evenly coated.
Spread mixture onto the prepared pan in an even layer.
Bake 25 minutes, stirring and re-spreading every 10 minutes until glossy and lightly crisp.
Sprinkle toffee bits over the hot mix and toss lightly. Cool completely on the pan until crisp, then break into clusters.