Design megas for the starters still without them. I'll start with some for gen 2, the best starters.

Typhlosion
Fire/Ground
Ability: Drought
HP: 78
ATK: 84 > 110
DEF: 78 > 88
SPA:109 > 135
SPD: 85 > 90
SPE: 100 > 135

New moves: Earth Power

Feraligatr
Water/Dragon
Ability: Adaptability
HP: 85
ATK: 105 >140
DEF: 100 >125
SPA: 79
SPD: 83 > 120
SPE: 78 > 81

Meganium
Grass/Fairy
Ability: Healing Aroma (auto-Grassy Terrain combined with auto aromatherapy on switch in/evolution)
HP: 80
ATK: 82
DEF: 100 >130
SPA: 83 > 120
SPD: 100 > 130
SPE: 80 > 83

New moves: Wish