How to beat the Bongcloud Attack
Develop fast and open the centre with ...d5 while White’s king blocks its own bishop and queen. Put a bishop on c5 aiming at f2, and the king on e2 or e1 soon becomes a target.
What they are after
White walks the king forward on move two, usually as a joke or to throw you off balance. The move blocks the bishop on f1 and the queen and gives up castling for good, so it is objectively bad; the only danger is playing too casually against it.
The answers
Open the centre with ...Nf6 and ...d5
The plan
Develop the knight to f6 and break with ...d5. After the trades on d5 your queen sits in the centre, and when the king walks back to e1, ...Bc5 aims at f2. Follow with ...Nc6, ...Be6 and long castling, and your rooks reach the open d file first.
Your chance
If White tries Qf3 to trade queens, ...e4 hits the queen again, and even grabbing g7 leaves White far behind in development.
Watch out
Don’t sacrifice on f2 without a clear win; with two extra tempi you can simply play good moves and convert.
Calm development when the king goes back
The plan
If the king goes straight back to e1, White has lost two moves and the right to castle. Develop with ...Nc6 and ...Nf6, strike with ...d5, then add ...Bc5 and ...O-O: you are playing an open game two full tempi ahead.
Your chance
After ...dxe4 the queens may come off, but White’s king still can’t castle and your rooks take the d file.
Watch out
A strong player may use the Bongcloud only to unsettle you; develop normally and don’t burn your clock looking for a knockout.