The rules say that if a surfaced Dragon enter the tile of another player, that player may attack the Dragon. This is clear enough for Knight and (Goblins sans Knight). But what about the Thief.
Can the Thief stand guard and get a free backstab in on the Dragon as it passes given enough stealth?
More to the point could a Thief one stashed treasure away from winning, stand at the entrance tile and pickpocket a passing surfaced Dragon and immediately stash it wining the game? I doubt it though I think this is a shame. I think it would be good.