1. e4 g6 2. d4 Bg7 3... c5
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what is this opening? is it just a transposition to a sicillian?
sniper as charlie storey would call it. most of the time it doesn't matter what white does as you can't really prevent g6 and bg7 and c5.
you can invite a benoni with 3 nf3 c5 4 d5, or some form of accelerated dragon if 4 nc3 cd.
however the critical line is
when black usually takes on c3 and then plays f5. it has the name "beefeater variation." it is a bad line for black but you have to play very sharply as white to show that.
otherwise black can transpose to a normal benoni or maybe a benko but if he wanted to play this way there doesn't seem to be a lot of benefit in choosing this move order
