From DominionStrategy Wiki
At the start of Clean-up, you may trash an Action card you would discard from play this turn, to gain a card costing exactly more than it.
 Official FAQ
- You can only trash an Action card that would be discarded this turn; you cannot trash a non-Action like Silver, or a Duration card that will stay out (but you can trash a Duration card that will be discarded).
- You can trash the Improve itself.
- The card you gain does not have to be an Action, it just has to cost exactly more than the trashed Action.
- Using this ability is optional, but if you trash a card then you have to gain one if you can.
 English versions
|+. At the start of Clean-up, you may trash an Action card you would discard from play this turn, to gain a card costing exactly more than it.||Renaissance||November 2018|
 Other language versions
 Secret History