I got this idea for a starter trio of a British Isles-based region.

Drathorn -> Guivine -> Rosagon
Type: Grass -> Grass/Dragon -> Grass/Dragon
Ability: Overgrow
HA: Intimidate
Base Stats:
50/62/40/68/40/60 (Drathorn)
65/82/55/88/60/70 (Guivine)
80/102/70/108/70/100 (Rosagon)
Moveset: Petal Blizzard, Draco Meteor, Flamethrower, Sludge Bomb, Petal Dance, Dragon Claw, Outrage, Poison Jab, Rock Slide, Synthesis

Foalit -> Burnicorn -> Centarmor
Type: Fire -> Fire -> Fire/Steel
Ability: Blaze
HA: Moxie
Base Stats:
45/60/45/55/45/70 (Foalit)
55/85/60/75/55/90 (Burnicorn)
70/110/80/75/75/120 (Centarmor)
Moveset: Flare Blitz, Smart Strike, Blaze Kick, High Horsepower, Bullet Punch, Swords Dance, Close Combat, Aerial Ace, Agility

Aqualet -> Swadance -> Torroyal
Type: Water/Flying -> Water/Flying -> Water/Fairy
Ability: Torrent
HA: Serene Grace
Base Stats:
50/40/55/50/65/60 (Aqualet)
60/50/75/70/85/80 (Swadance)
80/60/95/90/105/100 (Torroyal)
Moveset: Scald, Moonblast, Hurricane, Aromatic Mist, Roost, Hydro Pump, Air Slash, Shadow Ball, Psychic, Ice Beam, Dazzling Gleam

What do you think?