the first G1 transformer I had trouble with was Megatron, at the ripe old age of maybe 5 or 6, I had to get help from my Dad. at least for the first time, just to figure it out.

I found the G1 decepticon clones to be very difficult to transform, the hands were extremely tight, I used to have to get something to use to pry them started so I could finish it by hand.

the 2007 movie leaders were quite hard the first time through, even Megs, mainly due to the fact that the final mode wasn't readily familiar.

I'm yet to open my ROTF prime and Jetfire 2 pack.

ROTF Deluxe Skids and Mudflap are definitely up there, very difficult, and the final robot mode is so rubbish that there's no satisfaction from the transformation. The icecream truck wasn't too bad though. better than the individuals.

ROTF mixmaster was extremely difficult, and the weapons platform mode was just a little too non-descript to be sure you had it right.

A lot of the ROTF figures were very complex but many of them were interesting more than they were frustrating. I think these designs pushed the HASTAK design team to new heights with what they were able to attempt, and this knowledge will only pay of for us in the future.

MP megs was a cracker, after a while I went back to it to transform it and had forgotten a couple steps, in the end I had to dig out the instructions to figure it out, I was so scared of breaking it otherwise.

Generations Lugnut, where the tail slides towards the chest in robot mode, mine always sticks and I invariably crush my fingers when it pops into place. I can't remember the last time I experienced so much pain transforming a figure.

Generations Frumble, was difficult to get back into data disk mode the first time, not having seen the arms rotated and not having instructions. (brilliant engineering, especially designing it so that someone would be able to assemble it without it exploding in their hands before it was finished. something that I'm sure they don't usually have to take into account.)