One of the classic ways to attack a castled king in a double king pawn opening will be covered in this article - King Safety and the Doubled f-pawn.
This situation occurs in the following situation
- Opponent's king is castled kingside
- Opponent's f6-knight is pinned by a bishop on g5
- Opponent's dark-squared bishop can not break the pin with ...Be7
- Our knight can jump into d5 forcing the opponent to lose a queen or accept doubled f-pawns
- BONUS: Opponent's pawn on h6 instead of h7
From my experience most players rated >1400 will be on the lookout for this attack and players in the 1000-1400 range may even play a premature ...h6 just to prevent it. The usual way to take advantage of this pin is to first capture (Nxd5) followed by Bh6, Nh4 and bringing out the queen.
If you're wondering how Black can prevent this attack the best line would have been kicking the bishop with 6...h6 and if 7.Bh4 g5! After witnessing this attack in games from two of my students in the past week I have been waiting to post an article about it.