(forbiddance rule isn't dnd specific but that's the context I'm working with so)

if they didn't cross the threshold willingly it's fair game right

related ideas:
-vampire throwing themself at an open door in an attempt to make physics work for them (won't work obviously but it would be funny)
-vampire riding in a vehicle with a (knowing) mortal at the reins (outcome: ???? this is deliberate but vamp is being carried inside)

bottom-of-the-barrel/least serious:
-cast protection from evil and good on vamp in hopes of keeping them from affecting themself (obviously won't work, suggesting caster clearly dumped int)

....gdi though I just thought of another funny/horrible one:
block all routes except into forbidden building, then turn undead. probably won't do anything but create an extremely stressed vampire

someone's getting bitten after that one

(these aren't for a current writing project but for something I'm toying with down the line)

I think turned undead that can't flee just cower in fear, so...yeah, extremely stressed vampire!

lol thanks for the confirmation!

"What do you mean, what am I doing? what's it look like I'm doing? ...I spent way too much gold on this portable catapult NOT to use it. >;{"

LMAO I love it

minion-flinging for perfectly legit reasons

it's fine, they regenerate!

Grapple check and attempt to drag the vampire over the threshold!

haha, yeah. I honestly think having someone else move them is the only way

But imagine if it doesn't work, and you're just shoving the vampire up against an invisible wall...

(Imagining a scene from an anime I watched recently, where a character has been trapped by a spell forbidding him from leaving an area and another character tries to pull him through because the forbidding force is invisible...)