Poison Ivy and the Joker are two very contradictory characters. Poison Ivy is seductive and sexy in a pretty deadly way and the Joker, well what can we say about the Joker? He's the most twisted motherfucker of them all and that's why we love him.
Here's what we did:
For the Poison Ivy costume (which is not that "instant", but all the more awesome), Melina used an old body con dress, sprayed it with glittery green fabric color and glued lots and lots of plastic ivy leafs on it. The rest -as always- is make up. As you can see she even glued some ivy leafs on her eyebrows. Be careful what kind of glue you use, because even though she used lash glue, it hurt pretty bad when she took the leafs of...Complete the look with red heels and green tights (if you think your knees are disgusting for example).
For the Joker costume, the best case scenario would be you having a purple velvet suit at home. But let's be honest here, who the fuck owns something like that? So instead just try to use as many purple garments as you have, or just one, if it's ugly enough (like Ago's blouse). Other necessities are a waistcoat and a tie and OF COURSE the creepy make up. There are hundreds of Joker make up tutorials out there, just take a look and last but not least, please don't use acrylic paint to color your hair, it's really hard to get off...