To advance in Aegis Cave, you need to collect Unown Stones I, C, and E first and talk to the statue, then beat Regice. Then Collect R, O, C, and K, talk to the statue, and then beat Regirock. After that, collect S, T, E, E, and L, talk to the statue, and beat Registeel. After that, get to the end and beat Regigigas and his 4 Hitmonlee and 4 Bronzongs.