Four-Player Chess/Common openings/1. h3/1...d6/1...h12
Modern Sicilian, 1...h12
Yellow develops on the opposite colour squares compared to Red and normally follows up with one of two main ideas. The first idea is Bg12, attacking Green's weak m6 square, which can potentially be very dangerous, although Blue and Green have the resources to defend adequately. The second idea is Qh13, developing the queen on the light-squared diagonal, possibly aiming to create mating threats against Blue, if Red's queen can attack b7 or b9 later on.
Green has several options. The most common reply is l9, the Kann Variation.
The classical choice, intending to blunt a bishop move to g12 with pawn to k8.
This opening move seemingly allows an annoying check, but in fact, it is very hard for Red and Yellow to take advantage. This specific move order has caught on lately, probably because of it's flexibility. Green and Blue can choose their set-up depending on what red and yellow will play. Specifically keeping the b8 pawn for Blue on the original square can be useful later, allowing Blue to play Nc6 and c7 or d7, countering the usual idea of Yellow to play Qh13. Another way to deal with Qh13 is for Blue to play c8 and for Green to answer the check with Bm8. This may look like a mistake at first sight, but in fact it is playable. If Red tries to set up a checkmate on Green by playing Qxm7+, Blue answers by playing Qxg13+, which is simply a queen trade.
The idea is to prepare l7 by defending the queen on n8. The approved way to counter this choice is for Red to play e3 and after Blue plays c8, Yellow plays Qh13. If Green now tries to play l7, it will backfire. The reason is that Red captures on n8. Since Yellow can capture the knight on l9, Blue has to play Qc9 to protect the knight, but then comes Qi12!. After Nxn8 the point is revealed with Bxb5, which wins quite easily. This way of playing was in fact introduced by valger himself, when some clever players tried to play Valger's defence against its creator! Of course, Green could refrain from playing l7, but then it can be quite difficult to activate the queen. Skilled manoeuvres will be required just to stay in the game.