Kain has tricked Dorian into believing the condoms he received from L for Christmas are balloons. With Dorian's help (the mummy's ignorance and knowledge of the helium cylinder he used for both Asgard parties were a plus), Kain has returned his gift to L.
If you should see a random "balloon" or two floating by, this is because of butterfingers Dorian, who accidentally let go of a few.
Just thought you guys should know. ♥