Nargott
Auto-translated
I believe that invisibility until the first detection would be the most appropriate. Specifically: the hero is invisible during the opponent's turn. That is, if the opponent reveals the area with him, he will only find out about it on the next turn. This is a kind of ambush invisibility, similar to lurkers or zergs burying themselves in Starcraft. And on the minimap, he would not be displayed, as he can be hidden for the duration of the opponent's turn.
And the inability to attack can be implemented as a separate feature.