Here is the full list of all 13 Tiny Troopers Joint Ops achievements worth 1,000 gamerscore.
Zombie - Got a full squad
Zombie - Reached wave 10
Zombie - Killed 100 zombie chickens
Lost the first mission in either Campaign
Completed the Tutorial
Complete the Soldier Campaign
Complete the Special Ops Campaign
Complete both campaigns
Use an airstrike to kill 3 enemies
Earn 1,000,000 Command Points
Fully upgrade your squad
Revive fallen squad members 10 times
Zombie - Reach wave 25