#5 on the countdown is "The Harley and the Ivy" from The Batman Adventures Holiday Special #1 by Paul Dini and Ronnie Del Carmen.
The concept behind this Christmas classic (the title is, of course, based on the Christmas carol, "The Holly and the Ivy") is that Poison Ivy decides to liven up the holidays for herself and for her partner in crime, Harley Quinn (this is early in their relationship - they had only barely been appearing together on the TV series) by using her mind control powers to capture one of the richest men in Gotham City... Bruce Wayne!
Ronnie Del Carmen just kills it in this story. He does such a marvelous job on so many set pieces, like them welcoming Bruce into their car or the looks on their faces when they begin their shopping spree. And a shopping spree is, indeed, what their first goal is with their now enthralled Mr. Wayne, who can't stop himself from doing Ivy's bidding, but boy does he want to...
How dark did that get? Isn't that awesome that Dini was able to keep the line in there that they were planning on murdering Bruce after using him? Daaaaaaark!
Okay, so now that he is out from under their direct control, a groggy Batman takes them on. Del Carmen once again shines in the action sequence, as his depiction of Ivy with a giant boxing glove is to die for.
However, in the end, they are ironically done in by a plant, or a tree, that is...
This was, of course, adapted into the Batman animated series later on and has become a very memorable episode of the series. I am pleased that it got so much attention from such a larger audience, as this was a really great comic book story. It also helped develop the Harley and Ivy relationship, which has been a great addition to both of their characterizations over the years.