This is a short article for a simple card.
Sentry is very powerful. Why?
- Like Masquerade and Junk Dealer, it can trash without hurting your buying power this turn.
- Because it trashes cards from the top of your deck, you don't lose a draw on drawing a card you don't want in your deck. The extra cycling is deceptively powerful. Compare to Lookout. It doesn't replace itself, but the cycling / filtering aspect makes it a strong $3 cost trasher.
Unlike Masquerade, Junk Dealer, and Lookout, Sentry can trash 2 cards at a time. In exchange for all these upsides, the pool of cards you choose to trash from is only the top 2 cards of your deck, compared to every card in your hand. That can make Sentry a high variance card. The difference between revealing 2 trashable cards and 0 trashable cards is pretty stark. Other trashers don't have this issue as much, because when you get to choose from your entire hand, you'll often have something
you want to get rid of.
Because of all these factors, hitting $5 early is especially important in Sentry games. You want Sentry as early as possible, which is true of most trashers, but in Sentry's case it's because your odds of revealing 2 bad cards is highest at the start of the game. Missing $5 doesn't just delay your Sentry by a shuffle, it makes your Sentry materially worse than it could have been. And again, this is true of other trashers, but the trash-only-from-the-top mechanic magnifies how much worse it gets. That warps the opening by a lot - don't disregard the usefulness of opening Silver.
If you can, you want to get 2 Sentries, but because Sentry's power decays as the game goes on, it loses to other $5 costs pretty quickly, and you often run out of time to buy the 2nd.
All the standard Cartographer synergies (Wishing Well, Herald, Mystic, Vassal) continue to apply with Sentry, but the trashing is the most important aspect of the card, and its what you should be keeping in mind when evaluating it.