I hoped to find some way to phrase this card so that it simply triggers on any Action containing a certain word or words, without triggering for an absurd number of Actions that have no meaningful interaction. No such luck. I searched for a variety of uses of the word "hand" on the cards. I have bolded the cards which are obviously meaningful possible interactions with Ghost Town.
YOUR HAND
"into your hand"
Adventurer, Apothecary, Explorer, Farming Village, Hunting Party, Ill-Gotten Gains, Mine, Native Village, Scout, Scrying Pool, Wishing Well
"from your hand"
Ambassador, Apprentice, Bishop, Chapel, Courtyard, Develop, Expand, Explorer, Farmland, Fool's Gold, Forge, Haven, Horse Traders, Island, Jack of All Trades, Masquerade, Mine, Mint, Moat, Moneylender, Remodel, Salvager, Secret Chamber, Steward, Spice Merchant, Trader, Trading Post, Transmute, Treasure Map, Upgrade, Watchtower
"in your hand"
Throne Room, King's Court
"reveal your hand"
Menagerie, Crossroads, Shanty Town
"discard your hand"
Minion, Tactician
HIS HAND
"from his hand"
Bishop, Bureaucrat, Ghost Ship, Governor, Masquerade, Tournament, Young Witch
"in his hand"
Ghost Ship, Militia, Torturer
"discards his hand"
Minion
NO PRONOUN
"in hand"
Followers, Ghost Ship, Goons, Library, Margrave
I like the way you've taken it, even though I miss Masqerade, Menagerie, Tactician and Shanty Town interaction.