D&D General An on the spot encounter.

[Creed2347]

So my players found their way into a flower garden on their way to fight the boss. The idea was to have no enemies and allow them to get a sneak attack on the enemies inside, but like any d&d group they did the unexpected and one picked a flower. So I decided to make an encounter out of it. When he picked the flower (color) rose musk zombies rose from the surrounding area and targeted the player who picked the rose. And later shot an arrow with a natural 1 so he hit more roses and summoned more rose musk zombies.
To clarify the zombies do not rise from the flower beds. And they target the person who took a deliberate act that caused damage to the flowers.

Example:

• character throws other character into flowers, zombies attack the thrower
• uses movement in the flowers, zombies attack that character
• shooting a bow or throwing something and hit the flowers (purposefully or not) attacks shooter/thrower.

Reason is, the flowers are a memorial garden for the lords dead wife and recently killed son, and the lord became a necromancer in an attempt to revive his son because it was the closest thing to resurrection he could think of. So the flower zombies where actually raised be him in anger for damaging the memorial.
All of this was made up in session except the becoming a necromancer to resurrect his son part.

What was a time you created an encounter on the spot because your players did the unexpected?

 

[Stormonu]

Playing in Saltmarsh. A player fell through a rotten piece of floor. I made a mistake on the map where they landed, so I had the room be an extra dimensional pocket that hid a Teleportation Circle back to Saltmarsh. They spent twenty minutes trying to figure out how to rescue the fallen character (“we can’t find a door to the room on the first floor, the room you’re in is locked, and the edge is too dangerous to try and get you back up”). The hidden Teleport Circle has also become a secondary mystery - so far, just about every major place they travelled to now has one hidden somewhere, and they don’t know whose made them - or why.

 

[MarkB]

So, we're in Eberron, and the party of four 10th-level characters are venturing ever-deeper into the Mournland. They've been in there for days now, over a few sessions, and they know that its chaotic effects are having an increasing effect on them as they go deeper. Spells they cast occasionally come to life, they've seen magic items that have become animated, one of them has even begun to mutate, gaining bestial traits, they know they're on a timer to get out of there before the effects become permanent.

But they have a mystery to solve, so they push on, coming to the edge of the Glowing Chasm, which seems to be a source of these corrupting energies. They peer over the edge and see a seemingly bottomless canyon lined with glowing purple khyber dragonshards like the inside of a geode, its walls teeming with various mutated insectoid creatures, themselves infested with crystalline growths, many grown to huge sizes. It's meant to be a wake-up call, that they've gone as far as they can now, and to proceed any further would be to get overwhelmed, both by the creatures and the corrupting energies suffusing this place.

And they get it, and prepare to leave, but not before one of them decides to rappel down the side of the cliff just far enough to grab some of the corrupting crystals as samples.

So, that's when the purple worm attacked.

They finally finished the fight with two characters in the worm's belly, one making death saves, and nobody on more than a dozen hit points. After which the character who'd gathered the dragonshards tucked them into their bag of holding, after emptying out its other contents.

Later, they found out what happens when you place chaotic, magic-corrupting dragonshards in a bag of holding and leave them there for two weeks. But that's another story.