How to Make It
Heat jars in simmering water until it's time to fill them. (Hot liquid may cause a room temperature jar to crack and/or explode.)
In a saucepan, boil Faygo until it's reduced down to 2 cups. Stir in water, sugar, and lemon juice until the sugar is thoroughly dissolved, and bring to a boil. Add butter to reduce foaming. Stir in pectin and boil furiously for 30 seconds while stirring. Remove from heat and skim excess muck from the top. Or don't.
Working one jar at a time, pour the liquid into jars leaving 1/2 inch headspace. (Note: A jar funnel significantly cuts down on mess and potential jelly-on-skin burn. You are a dope-ass ninja, but you are not immortal—yet.) Wipe the rim, place the lid on and close the band finger-tight. Return to the water and process for five minutes.
Let the jars cool for at least 24 hours before checking how the jelly has set. Depending on the beverages used, this may take up to two full weeks.
Note: Do not despair if the set is much softer than commercial jelly. Full sugar beverages fare better, and high-fructose corn syrup is a wild card. Then again, so are you, fam.