Someone looked into the ORAS demo files, there's one more Mega apparently hiding in the game code,
can you guess who it is?
Also, the stats of the Megas:
Index: 799 - Swampert-M Stats: 100/150/110/95/110/70 Type: Water/Ground
Index: 800 - Sceptile-M Stats: 70/110/75/145/85/145 Type: Grass/Dragon
Index: 801 - Sableye-M Stats: 50/85/125/85/115/20 Type: Dark/Ghost
Index: 802 - Altaria-M Stats: 75/110/110/110/105/80 Type: Dragon/Fairy
Index: 803 - Gallade-M Stats: 68/165/95/65/115/110 Type: Psychic/Fighting
Index: 804 - Audino-M Stats: 103/60/126/80/126/50 Type: Normal/Fairy
Index: 805 - Sharpedo Stats: 70/140/70/110/65/105 Type: Water/Dark
Index: 807 - Steelix-M Stats: 75/125/230/55/95/30 Type: Steel/Ground
Index: 808 - Pigeot-M Stats: 83/80/80/135/80/121 Type: Normal/Flying
Index: 809 - Glalie-M Stats: 80/120/80/120/80/100 Type: Ice/Ice
Index: 810 - Diancie-M Stats: 50/160/110/160/110/110 Type: Rock/Fairy
Index: 811 - Metagross-M Stats: 80/145/150/105/110/110 Type: Steel/Psychic
Index: 812 - Kyogre-P Stats: 100/150/90/180/160/90 Type: Water/Water
Index: 813 - Groudon-P Stats: 100/180/160/150/90/90 Type: Ground/Fire
Index: 814 - Rayquaza-M Stats: 105/180/100/180/100/115 Type: Dragon/Flying
815-820 are Cosplay Pikachu forms
Index: 821 - Hoopa-M Stats: 80/160/60/170/130/80 Type: Psychic/Dark
Index: 822 - Camerupt-M Stats: 70/120/100/145/105/20 Type: Fire/Ground
Index: 823 - Lopunny-M Stats: 65/136/94/54/96/135 Type: Normal/Fighting
Index: 824 - Salamence-M Stats: 95/145/130/120/90/120 Type: Dragon/Flying
Index: 825 - Beedrill-M Stats: 65/150/40/15/80/145 Type: Bug/Poison
MegaSalamence is confirmed to be broken (120 speed? Goodbye metagame). Beedrill also looks really good!