Battle-Combo Pledge Moves - Pokemon X and Y

There is a move tutor in Laverre City who can teach any starter Pokemon a their elemental "Pledge" move, for example;

Chespin & Bulbasaur - Grass Pledge

Fennekin & Charmander - Fire Pledge

Froakie & Squirtle - Water Pledge

The base attack of the move is 80, but when in a double battle with different start types using their element Pledge moves together the power increases to 150.

Grass & Fire - Sea of Fire which makes all non-fire types lose 1/8 of there health.

Fire & Water - Rainbow which increases all status effects likelihood of happening.

Water & Grass - Swamp which halves all speed.

Kanto & Kalos Starter Pokemon