It would be funny if in Phineas & Ferb, the one time Candace decides not to get her mom and bust her brothers, Linda shows up and notices Phineas & Ferb's invention on her own and grounds them.
The ultimate cosmic joke in Phineas and Ferb would be this: After Candace spent all summer sprinting across town, screaming “Mom! Mom! MOM!!!”, building elaborate schemes just to expose her brothers, she decides, for once, to not bust her brothers, and not ruin their fun. To just let Phineas and Ferb do their thing because it wouldn't matter since their invention would always disappear and she always looks like a fool.
And the moment that happens, Linda comes home early by choice and now she see the giant invention of the day in full glory and she actually processes it. Then the most terrifying line in the entire series is spoken: “Phineas. Ferb. What is going on here?” The grounding would be legendary. Not just “you’re grounded,” but full nuclear mom mode. Summer canceled is for the two, electronics confiscated, and chores for the rest of the summer. Candace standing in the background with the most haunted “I didn’t even do anything this time” face while her brothers finally get what she’s been trying to give them for months.
Linda also on the same day coincidentally decides to now check her bank account again after a while and finally sees all the money and loans Phineas & Ferb claimed through her to build their stuff. Her face slowly changes as she sees it: Hundreds of thousands of dollars in mysterious loans and withdrawals, payments to “exotic materials suppliers,” “quantum physics equipment,” “illegal fireworks wholesalers,” credit cards maxed out in her name, second mortgages she never signed for, a loan for a freaking rollercoaster in the backyard. The color drains from her face and she says, “Phineas. Ferb. What did you do?!”
The grounding would just be legendary. The boys would be grounded until college and their inventions confiscated and destroyed. Ferb would speak just to say “Well, this is unfortunate.”
Candace would be standing in the corner having a silent existential crisis realizing that the one time she showed mercy, her brothers got obliterated, and she didn’t even have to lift a finger. The ultimate irony: Candace spent all this time trying to expose them and failing. The moment she stops trying… the universe does it for her in the most devastating way possible.