Watchtower
Will only be played:
- if player has less than 7 cards in hand and the deck is not empty
When about to gain a card and still in hand:
- if the card is a Copper or worse it will be trashed
- if the card is a useless green that doesn’t want to be trashed, do not reveal
- if the card is anything else put it in top of player’s deck
Geronimoo's Dominion Simulator 
Could the play priority of the watchtower be made variable in the same way as a smithy? I’d suggest that it should be the lowest priority action if there is only one action remaining (or 6 or more cards in hand) and keep the current priority action otherwise.