So Dark Ages obviously has a lot of cards with on-trash-benefits.
The attack cards Swindler, Saboteur, Knights and Rogue are a lot weaker on boards with such cards.
I was about to make a posting evaluating Knights in another thread, so I thought I'd make a list of the new cards that have on-trash-benefits first to see just how many there are. Maybe someone else will find the list useful as well:
$2:
Squire (The cost of only $2 means that Knights, Rogues and Saboteurs won't trash them.)
$3:
Market Square (no benefit when trashed itself, but possible benefit when a player has it in hand when something else gets trashed)
$4:
Feodum
Fortress
Rats
$5:
Catacombs
Cultist
$6:
Hunting Grounds (If trashed early in the game, this could actually be an on-trash-drawback instead of an on-trash-benefit. But I think on most Province boards, it should be more of an advantage than a disadvantage to get a free Duchy for the larger part of the game – and Hunting Grounds cannot be trashed before the second reshuffle because of the cost of $6.)
So that makes 8 different cards in total (only 7 which are relevant for Knights, Rogues and Saboteur).
I did not include Hermit and Urchin in the list because they don't provide benefits when they are trashed by any other card (be it from the opponent or oneself), but only offer their benefit when they are trashed by their own special ability for that.