Here is the full list of all 8 Mount Your Friends achievements.
Spin 5 times in air before landing on any surface
Have a climber 40 feet away from any other climber in Man Crafting
Make a tower 70 feet high in Basic Climb without climbers taking up more than 7 feet of the field's width
Make a pile of 10 climbers in Basic Climb without passing 11 feet
Have your top 2 climbers at least 60 feet up and 60 feet apart in Basic Climb
Travel 50 feet horizontally without sticking to any surfaces
Make a tower of 6 teabaggers in Basic Climb
Have 8 climbers in Basic Climb chain holding hands