Apprentice is a good end game card when you can trash other action cards which have outlived their usefulness to crawl your way to those last couple of Provinces.
Not only the obvious Sea Hag, but also small utility cards like Caravan are ideal for this.
You can often trash your Potion as well if it's not a Vineyards or Alchemist game.
Other things that can be good:
*Trashing a Province for 8 cards might well be good enough to buy you another Province in addition to what you would have bought anyway. This can let it act like Remodel, Salvager, and the various other cards which can trash and replace a Province to accelerate the game end.
* Cads with on-gain benefits. Once in your deck they look overpriced. Border Village is a good example: many times you only took the BV because it was free, and you won't miss it at all when it's gone. Same for that Duchy you bought with your Hoard (sometimes the Gold too).
* Pretty much any inexhaustible source of $4 or higher cards can be good. Ironworks, Fortress and Rats (which is effectively $5), etc. Obviously other cards with on-trash benefits are nice too.
Of course there's a lot more to be said. And a lot of this goes for other TfB cards like Remodelers, Bishop, etc. as well.