Megatron versus Iron Man
my favourite Transformer from back in the days of the Transformers movie (well, Galvatron's awesome too but Megatron's the original), versus one of the least interesting comic characters I've read, a guy with a tin suit and lots of lasers, rockets and guns.
no particular scenario or battle plan. Iron Man just sees a massive robot flying in the sky, decides to challenge it. Megatron just sees a small tin suit flying right at him, so decides to have at it.
personally, I'd expect Megatron to just blast him out of existence, but then I've never read much of Iron Man, so who knows what tricks he's got up his sleeve.