Do you have any mischievous mythical creatures in your culture?

[Winner]

In Slavic mythology, a rusalka (plural: rusalki) was a female ghost, water nymph, succubus or mermaid-like demon that dwelled in a waterway.

This.

Also:

hejkal - "howling creature", lives in deep forests and scares people by producing howl-like sounds. Usually not seen, though it's known to take shapes of trees.

vodník - "water sprite", lives in ponds and small lakes. Usually drowns people who want to swim there and collects their souls.

klekánice - "vesper bell hag", a spirit-like creature looking like an old ugly woman. Kidnaps children who are still hanging out after vesper bell.

polednice - "noon hag", a variant of the vesper bell hag - looks the same, only takes children at noon.

Yeah, it used to be dangerous to live here

 

[RedRalph]

We have water sprites too, and the Scots have a horse version of it called a Kelpie

 

[Winner]

We have water sprites too, and the Scots have a horse version of it called a Kelpie

I am sure these creatures exist in many national variants across Europe.

 

[Love]

In sweden it's Rået!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Translated to "Raw"

 

[SS-18 ICBM]

Quite a lot of mischievous creatures in Filipino mythology. The nuno sa punso (lit. "grandparent/ancestor of the anthill") will harm or injure anyone who does harm to its anthill. The duwende (dwarf) is a playful creature that shows itself to children. Come to think of it, most of the mischievous creatures in this mythology tends to engage in harmful behaviour.

Nuno sa punso

Also, at the "jailbait" tag.