Here is the full list of all 33 Marshmallow Madness achievements.
Defeat your first Marshmallow
Explode your first barrel
Complete your first wave
Burn your first Marshmallow
Get burnt once
Get destroyed by an explosive barrel once
Push a Marshmallow from behind
Push a Marshmallow off the world
Defeat 10 Marshmallows
Defeat 50 Marshmallows
Defeat 100 Marshmallows
Defeat 500 Marshmallows
Defeat 1000 Marshmallows
Defeat 5000 Marshmallows
Defeat 10,000 Marshmallows
Explode 10 Barrels
Explode 25 Barrels
Explode 50 Barrels
Explode 100 Barrels
Reach wave 5
Reach wave 10
Reach wave 30
Reach wave 50
Burn 10 Marshmallows
Burn 50 Marshmallows
Burn 100 Marshmallows
Burn 500 Marshmallows
Burn 2500 Marshmallows
Push 10 Marshmallows off the world
Push 50 Marshmallows off the world
Push 100 Marshmallows off the world
Push 1000 Marshmallows off the world
Push 5000 Marshmallows off the world