Sun Tzu said that spies are the most valuable assets in warfare. Onimaru said that too. In Codex, the Flagstone spy is invisible, which is even better than the stealth ability you’ve seen before. Units and heroes that are invisible, like those with stealth, can sneak past enemy patrollers. In addition to that, invisible things can’t be targeted by enemy spells or abilities and they can’t be attacked in combat either. Opponents need a detector to see through invisibility, but those are hard to come by. They could also build the Tower add-on to detect one invisible thing per turn, though they can only have one add-on at a time.

Flagstone Spy is threatening to deal 3 damage to a building every turn. That, plus your other tricks is probably enough to repeatedly destroy a tech building, which is hugely crippling. He’s also gaining information about your opponent’s hand, letting you see which cards they teched from their codex. On top of all that, Flagstone Spy steals a gold if they have any gold in their reserves. Opponents simply MUST answer him somehow to avoid being dismantled, but he’s actually pretty hard to stop.

For a completely different line of play, look at these two Peace tech II cards: