Well, the trick with merging 'Wirt' from 'Over the Garden Wall' and 'Beatrice' from 'The Owl House' is that both shows share this weird, woodsy, folklore vibe, but their tones are miles apart. One's a melancholic autumnal fairytale, the other's a chaotic magical dimension comedy. I've seen a few attempts that just drop Wirt into the Boiling Isles, and it usually falls flat because he'd just... panic and shut down. What makes a plot click for me is when the crossover respects Wirt's core conflict—his anxiety and self-doubt—and forces Beatrice to navigate it. She's all bluster and practicality; she'd get so frustrated with his hesitance. A compelling plot might reverse their roles: instead of a portal, maybe the Unknown bleeds into the Demon Realm somehow, and Beatrice, now human again, finds herself lost in its symbolic woods. She'd have to rely on Wirt's hard-earned, gloomy wisdom to survive a landscape that reflects his inner world, while he has to step up to guide someone even more stubbornly lost than he was. Their dynamic wouldn't be romantic for a long while, if ever; it's a survival partnership where her cynicism clashes with his poetic fatalism. The compelling part is the character erosion and growth—Beatrice learning there's value in quiet reflection, Wirt learning that assertiveness isn't the same as arrogance. The plot almost writes itself if you anchor it in that fundamental mismatch.
I'd avoid just making it a 'team-up adventure.' The crossover's strength is in the contrast. Maybe the Beast's influence is a kind of magic that even Belos couldn't control, or the edelwood trees start growing in the Boiling Isles, draining magic instead of hope. Beatrice, recognizing a predatory system, would want to fight it head-on, while Wirt, who understands the Beast's deal all too well, would know you can't just chop it down. That creates immediate, organic conflict. The resolution shouldn't be a big magical battle; it'd be something quieter, something that uses the themes of both shows—maybe sacrificing a different kind of 'fuel,' like a cherished memory or a bit of personal magic, to rebalance the realms. The ending feels earned if they both leave changed, not just if they save the day.