One of my favorite D&D gags that I ever came up with is part of a oneshot I've run a few times where the party is hired by a young wizard to help clear out a few active security measures in a tower that the wizard inherited from her old teacher.
The first obstacle to be cleared is the re-animated skeletons that the old wizard was using for gardening help. It's a pretty straightforward fight, but during the encounter, players may notice one particular raised bed of herbs that is set back in a corner of the garden by itself.
Upon further investigation, this one raised bed is absolutely shining with magical protections. There are runes carved into the wood of the bed, gemstones inlaid in the top of it, this bed is absolutely protected out the ass... and an arcana check shows that the protections are all pointed inward, attempting to keep what's in there from getting out.
What's growing in that raised bed, you may ask? What is so dangerous that the old wizard felt the need to place all these protections?
Mint.