I'm not sure if I'm just not getting the trick - that was the case with many other special battles... However, I'm really not getting the one where you have to get 3 gold wagons within 3 rounds (from the bandits near the monastery). Any tips?

How do i do that? I dont know how to attack with my units except with arbalests and they do barely any damage at all, my other units do nothing but stand around and die.

So, managed it yesterday. I think the instructions are pretty shit in general, I keep not getting puzzles because they're not exact.

You don't need to destroy all wagons - you only need to prevent 3 from escaping in the limited round time.
In fact I believe destroying 2 was enough. So the first one you likely won't get. Then destroy 2 more with the conventional tactics (Wagenburg + many cards for damage, or Arbalests).

I'm not sure if there's a step-by-step process. I know for example that the first one can be destroyed quite easily: put Wagenburg, then War Wagon (which gives the Wagenburg 3 armour), in the same turn move the Lyrian Banner to the line with the Wagenburg (+1 Arm) and boost it with Meve's sword (+1 Arm). Fire away at the gold wagon for damage. Next turn, use the Arbalest on the row with the most cards for another 5 damage, - and the gold wagon's dead.

Okay, so there are two goals in the battle - the first is destroy three of the escaping gold wagons. The second is win the round with a higher point total as usual.

I waited to the very end of the chapter to do this fight as I found it very difficult. By then I had Meve: Rivian Broadsword, Eyck of Denesle, Maticore Trophy, Fake Floren, Lyrian Arbalest + and other good cards that I didn't have when I first came across the battle.

I led by placing the Manticore Trophy

The first gold wagon to come out was hit by the Manticore Trophy, then meve: rivian broadsword. Then I planted a War Wagon I believe I attacked again with a arbalest +, but don't remember. This wagon escaped.

I recalled The war wagon with a decoy and replanted it to get more Light infantry. They help for making arbalest stronger and when destroyed inflict 5 damage to a random enemy.

The first gold wagon i destroyed was instantly taken out by a powered up Eyck of Denesle The second to go by a combination of Meven and arbalest. The final by arbalest.

I have a lot of arbalest + in my deck and regiment drummers. When the final wagon came out the regiment drummers had all performed their order so I played Reynard Odo, which was one of my last cards, hoping to draw more arbalest from the regiment drummers renewed orders. The Manticore Trophy helps out a ton as every card the opponet plays get damaged when it comes out, even if only by a little, it also helps Eyck power up fast which will guarantee he can kill a gold wagon at some point.

Hope all that helps with some strategy!

That's the thing, you don't need to destroy three gold wagons. 2 are enough.
Not sure if you'd get a higher reward if you destroy more?..

Just started this playtrought, after 3 hours finding out how to destroy all the gold wagons, I only found a solution for 3 wagons.
using the beginning deck it is possible, but you need to have a perfect hand.