Lance's second battle was ridiculously difficult, even though I specialized in Ice (And Poison, by the by) types. Could just be a combination of the fact I'm the unluckiest person to grace a DS, but his Salamence's Fire Blast hit me with a critical hit, FIVE times in my first run against his second team.
Other than that, I remember suffering under the cruel brunt of Lucian as his Bronzong squished my team over and over until I finally relented and became a multi-typist.