These took me THREE years to collect 100%, meaning they came sealed in their package with their corresponding sticker and insert. Sorry if the pics are kinda murky but I live in a fricken cave; I lighten them a bit with PS.
The Battle Museum figure (black base) comes with two stickers to be placed at the front and back of the base. The front says Gengar (ゲンガー) and the back is, what I assume, two attacks but I can't read an ounce of Japanese. This one I've actually seen a few times being sold with at least the correct name sticker already on the base.
The Full Color figures (the two right ones) DO NOT have corresponding stickers. These just come with the base.
FC Stadium figures (middle ones) DO come with stickers. The Night Shade Gengar was the hardest to find.
Below is the complete checklist of ALL the Full Color figures. You can click to make it larger
This awesome blog features most (if not all) of the FC Stadium and Battle Museum figures:
http://tmhrcork.blog52.fc2.com/blog-category-9.html - FC Stadium
http://tmhrcork.blog52.fc2.com/blog-category-10.html - Battle Museum
That blog was of great help because I didn't really know how many of these Gengar had until I found it by mistake; a lot of respect to this Japanese blogger.
I was able to get four of these figures from the same seller at different times on Yahoo!Japan auctions.
Some tips for finding these figures.
These figures are not really that rare by themselves. You can easily find the figure by itself in lots or being sold for cheap. Then it won't take you three fricken years lol.
I was out to find these 100% complete and it most likely means you have to find a sealed set; that's when they become hard to find.
I've seen some sets of these on Ebay but I never see the Battle Museum ones on there. You will most likely have to get these from Japan and they might even be cheaper.
The highest I've paid for a lone complete part is around 2,500 yen (~$25). This was approximately a year and half ago from this post. The lowest is 1,000 yen (~$10).
The last set that contained the Nighshade Gengar (the one to the left of the Lick Gengar), was in a lot that costed 8,500 yen (~$85). It came with 10 sets but some were incomplete and even only containing two figures.
The Japanese words I used to search for the sets are in the first paragraph of this post.
You might get lucky and find one with the correct base and sticker by itself! This has never personally happened to me, though.
It's so rewarding to finally have these little guys! It's one more thing I can finally stop searching for.