A few picks:
TM2 Megatron's Dragster mode:

I could probably count the amount of times I've transformed Megatron this way on one hand. Maybe I'm exaggerating, but it can't be more than two hands. This is just...dumb, and you can't even properly transform the figure this way right out of the box. True it's an extremely simple fix(unscrewing the blue piece on the back of the neck and flipping it around), but it's the principle.
Armada Thrust's hurricane attack mode:

I'm going to guess at least one person reading this didn't know this was a thing. You turn the head around, extend the back section a little, and attach a mini-con to the chest to pull a lever that results in...his wings hitting his knees and not even working most of the time.
Universe 2.0 Galvatron's infamous tank mode:

*Edit*D'oh! Pic doesn't appear to be working, link to Hasbro Q&A page where it's shown: http://www.toymania.com/news/messages/10873.shtml
This is what spurned the thread, because I remembered this was a thing and looked up the picture to try it again. And you know what, it looks silly, but the deluxe can technically transform like this, though slightly slanted. And I like the crazy thing! I think it's great that an abandoned feature is still viable, and it reminds me of a certain walking nuclear death mobile.