Quite a while ago now, I had an interesting discussion with kylemeister about a line of the Cozio which NCO treats as a Cozio Defence Deferred, namely 1 e4 e5 2 Nf3 Nc6 3 Bb5 a6 4 Ba4 Nge7 5 0-0 g6 6 c3 Bg7 7 d4 b5 (on 7 …ed 8 cd b5!?, 9 d5! is strong, but 8 …0-0!? 9 d5!? Na5 is interesting) 8 Bb3 ed 9 cd 0-0 (9 …Na5 and 9 …d6 will probably transpose) 10 Nc3 Na5 11 Bc2 d6 12 h3 and now 12 …b4, 12 …Bb7, 12 …c5 and 12 …d5 all look playable. In the meantime I’ve generated a few thoughts and questions.

Instead of 8 Bb3, 8 Bc2 is a critical try for advantage. Kylemeister pointed out that Iordachescu had suggested 8 …ed 9 cd 0-0 10 d5 Nb4!? (10 …Na5?! 11 a4!) 11 Bb3 a5. But is there, I wonder, anything wrong with 9 …d5!? here instead of 9 …0-0? It’s only been played twice, both times by untitled players. Both games continued 10 e5 0-0 which looks OK, but maybe 10 …Bg4 is still better. Alternatively 10 ed Nd5 and 10 Nc3 Bg4 seem fine though very complicated -- if White can advantageously attack I can’t see how. Is this line OK, or am I missing something?

I’ve also come to feel Black should probably play …Nge7 on move four. I like 3 …Nge7 4 d4 ed 5 Nd4 Ng6!? for Black, but why don’t the authorities mention that with 4 Nc3 g6 5 d4 ed 6 Nd4 White can transpose into the (advantageous) 4 d4/5 …g6 line? Instead 6 Nd5 is usually given without comment, but this too seems dangerous for Black -- aren’t the 10 Qd2 lines promising for White, or am I out of date? With …a6/Ba4 inserted, 5 d4 ed 6 0-0 g6 7 Nd4 Bg7 gives Black extra options compared with 4 d4/5 …g6, while on 6 Nd4 here I presume 6 …b5 7 Bb3 Na5, or 6 …Nd4 7 Qd4 b5 8 Bb3 d6, are OK. Finally, Cozio specialists Mozes and Varga meet 5 Nc3 with 5 …d6!?, defending(?) after 6 d4 b5 7 Bb3 Nd4 8 Nd4 ed 9 Qh5 Ng6 or 9 Qf3 Be6. 

Anyone got any thoughts on any of these lines, or do OFWATA or any other sources offer any improvements/refutations?