I know I said this in another thread, but I just want to get this out...
Lilligant
I always thought Lilligant would get the Fairy type in X and Y but I was proven wrong when its evil cousin Whimsicott got the typing instead. So maybe when or if Lilligant mega evolves, she will get the fairy typing with boosted special attack, defense, special defense, and speed with the ability Magic Guard to prevent effects from burn or toxic spikes, or keeps Own Tempo for more Petal Dance shenanigans. Also, give her access to moves like Moonblast, Dazzling Gleam, Draining Kiss, and should not let Sleep Powder be a pre evo exclusive or better yet give her spore (cant think of better moves atm)
Anyways Mega Lilligants base stats would be
Type: Grass/ Fairy
Hp: 70
Attack: 60
Defense: 75 -> 95
Special Attack: 110 -> 130
Special Defense: 75-> 105
Speed: 90 -> 120
Hydreigon
Next is Mega Hydreigon. I think Gamefreak should go back to Hydreigon's original concept and make it Steel/Dragon just to give it a chance against Fairy types that completely wrecked Hydreigon this generation. However I do believe Mega Hydreigon would keep the ability Levitate keeping its immunity to ground *cough* mold breaker excadrill *cough. Since the Steel Typing is normally a defensive type, I can see Mega Hydreigon gaining more bulk to survive more hits and a decent boost to its attack and special attack at the cost of its speed like mega garchomp or a very small boost of speed. For added moves, Hydreigon already has Flash Cannon and I can see it getting moves like Iron Head, Iron Tail, Magnet Bomb, or Steel Wing in the near future.
Type: Steel/Dragon
HP: 92
Attack: 105 -> 125
Defense: 90 -> 120
Special Attack: 125 -> 135
Special Defense: 90 -> 120
Speed: 98 -> 108
Samurott
Many people wanted Samurott to get a fighting type but I dont think that would work well on him to well so like Hydreigon, I believe Mega Samurott should get the Steel Type as well. And before you say anything about Empoleon, we have 3 FIRE/FIGHTING starters so saying Samurott cant get it Steel because Empoleon is not a valid reason. Plus Fighting has been taken by Emboar. Now back to the topic. I can see Mega Samurott getting big boosts to his Defense and Special Defense stats along with his Attack and Special attack. Or change nothing with his offenses and give him more Defense, Special Defense and Speed. Extra moves to learn would be Iron Head, Shell Smash Flash Cannon, Calm Mind, Earthquake, or even Dragon Pulse (he gets dragon tail so why not). As for an ability, there are many ablities that they can give to Mega Samurott, however I can see it either being Intimidate or Shell Armor
Type: Water/Steel
HP: 95
Attack: 100 -> 120
Defense: 85 -> 115 or 105
Special Attack: 108 ->128
Special Defense: 70 ->100 or 110
Speed: 70 -> 110