At the top of the image, "Erin the Human’s finally Level 18 — let the algebra of adulthood begin (minus the homework)!"

– Depict a playful Adventure Time-inspired scene where Erin is reimagined as a cartoon heroine with a trusty sword made entirely of glittery birthday candles, wearing a party crown, riding on the back of a giant grinning rainbow cake creature (think Jake the Dog in cake form).

– Floating nearby is a cartoon-style "18" balloon wearing sunglasses and looking smug.

– In the background, the Land of Ooo is decorated with confetti cannons going off and funky streamers tangled in Lumpy Space Princess's hair as she shouts, “Whateverrr, I invented being 18!”

– BMO is DJ-ing on a floating cupcake while Finn and Jake are seen cheering and holding a "Welcome to Adult-ish-ness!" sign.

– Add festive bursts of color and a sprinkle of absurdity, making it clear that turning 18 with this much Adventure Time energy means things are about to get math-magic-cool.

Generated with these themes: Adventure time themed, 18 year old, and Happy birthday.

Made with ❤️ by AI.