There's really only one I can remember, and it honestly only came to be due to my own over-confidence and bad positioning. Thankfully, I managed to take some screenshots at the end of the battle. I honestly don't remember specifics very well as I was so focused and in the moment that it all kind of blurred together afterwards, but this is how it went down as far as I can remember.
I was using the MOS submod and playing as Isengard. As is to be expected, battles with Rohan broke out quickly. This particular battle was one containing 3353 of my Uruks and Snaga, led by Lurtz, and just over 4000 of their Humans. Now, usually when seeing those numbers you'd think "Well that surely can't be all that difficult", and usually you'd be correct, except I made blunders on the campaign map and on the battle map that made it far harder than it had to be. I usually prefer to fight a defensive battle, and as such on the campaign map simply waited until they attacked me. This meant that they had time to completely surround my army with lots of smaller armies of theirs before finally engaging me. This was all well and good. I figured I'd be able to pick off smaller packs of them as they grew closer and it'd be an easy win.
With this in mind, when I spawned in I made sure to deploy my army near a side of the map I knew some of their men would be coming in. It turned out that their most substantial force would be coming in right near my army. This was a force of 1672 and was led by Egbert. Usually it'd be easy enough to destroy the army as it came in, but due to my bad positioning and the exact area of the map they came in, it was made a lot harder. You see, their army was split as it came in by a hill, which meant that some came in atop this hill and some came in below it.
The hill I'm talking of can be seen in this image (the image messed up a bit when I took it with FRAPS for some reason):
As you can probably tell from the image above, this was bad for multiple reasons. The first was that I didn't have time before they entered the battlefield to get up to the top of the hill, and the second was that I couldn't cut off the ones coming in below the hill without exposing my back to every other force they had coming down on me, especially the one coming in at the top of the hill. So what I did was set up my forces so that some of my Uruks were facing the edge of the map and awaiting the Rohirrim, while the rest were turned and awaiting the rest of their forces. By this point I'd judged it too late to move to a better location, and as such I was forced not only to fight multiple forces coming from multiple directions, but I was also fighting mainly uphill. But, due to my own blunders, there was nothing I could do by this point except try and make the best of it.
Here it where it begins getting fuzzy and I don't remember specifics, but this is what happened as far as I remember. My entire line was engaged and swamped with Humans. The fighting was tough, brutal and deadly. It even got to the point where I was forced to bring in my archers and skirmishers, and as I'm sure you all know, Snaga - especially archers and skirmishers - aren't the best melee combatants.
This went on for some time, me struggling to hold on and them doing everything they could to destroy me. At some point I decided "This battle is looking like it's lost, so I'm going to do everything I can to take as many of them with me as I can." So I kept on fighting. Eventually, it wound down. Thousands had died on either side and I was left with a pitiful force that involved 7 units, all with under 10 Uruks left. One group of Reavers, five groups of Uruk Raiders and Lurtz's Regiment. They had quite a bit more left than me, but they were mainly archers. High quality archers, but still archers. I think they also had a few units of a General's Bodyguard left as well, so I also had cavalry to contend with.
The rest of the battle involved me grouping the battered remnants of my forces and charging back and forth. First I threw all my forces at any force that they could get their hands on, which just so happened to be archers that outnumbered them. Thankfully they could fight far better than these archers and they routed them rather quickly. Once this was done, a game of cat and mouse began. I'd send my troops at their remaining archers - I can't remember what they were called, but they were high quality ones - while keeping an eye on the remnants of their cavalry. Whenever their cavalry tried to charge me I had to disengage from the archers and charge at the General's Bodyguard. Eventually I routed them and turned on the remaining archers.
When finally they routed and I was victorious, only twenty-five Uruks were left standing. Some 500 were on the ground injured and would manage to recover, but they were not the heroes of this fight. After all was said and done, this is what the Uruks left standing looked like:
Not at all a formidable force. You'll notice that slightly to the right of center, Lurtz stands alone. Every single Uruk in his regiment was slain during the battle, and by the end he was simply one Uruk among a handful.
This is what the field of battle looked like when the dust had settled:
In the end, it was a victory. Close, but a victory nonetheless: