First, he castles too soon, after 6.-Bh6 the move 6.-0-0 ?! deserves a doubious mark, he castled into it, now white can open the deathly h file for example due to the abscence of the Fianchettoed bishop (White can exchange it at pleasure).

Later on, white manage to get some regular moves in this variations, for example, after 7.-...Qa5, f3 has a double function, first of all it threaths to start a pawn storm by g4, h4-h5 etc, and next, it sets a trap, after 8.-...b5, 9.-Kb1 now white is menacing with winning a pawn, for making it clear, lets suppose black wants to have the vital b4 square for his knight and plays Na6, then

9.-...Na6?
10.-Nd5 Qd8
11.-Bxg7 Kxg7
12.-Nxf6 exf6 (Kxf6 seems Really bad in view of 13.-13.-Qh6, and basically white is much better due to his pawn structure.

But a knight on the enemy field can be trapped say's black, and knowing that he plans to frustrate white's intention and trapping his knight by

10.-...Qxd2?
11.-Nxe7+ Kh8
12.-Bxg7+ kxg7
13.-Rxd2 Bb7 (otherwise, if he let white exchanges the knight he would be a pawn down without compensation)

14.-e5 Ne8
15.-exd6 Nxd6
16.-d5! keeps the extra pawn.

Then, the greatest mistake, 14.-...gxh5? breaked completely the defenses of the king, however, black was already in a bad position.